# Goodman HP defrost question



## Bob Sanders (Nov 10, 2013)

Don't know if I'm doing this year or next but at some point I will be converting my Goodman timed defrost over to demand and I need to come up with a design for it. The question I have though since mine is a 2 stage is whether or not Goodman is using both stages during a defrost cycle, or just one. I would think it's both stages but I could be wrong.


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## user_12345a (Nov 23, 2014)

Would it make sense to find another two-stage heatpump demand defrost board for another manufacturer's heatpump and rig it up?

It would obviously have to support reversing valve energized in cool mode and the same type of condenser fan motor. Some of the higher end 2-speed heatpumps may have a ecm condenser fan motor rather than two speed.


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## Done That (Apr 28, 2011)

Goodman 2-stage heat pumps defrost with compressor running on high to get the job done as quickly as possible.


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## digitalplumber (Jul 8, 2011)

How important is this feature: Timed vs demand? 

I am not familiar with heat pumps and the system possibly slated for MIL's house is a Bryant and it only has "timed".

Is this more important in a high heat demand climate such as Canada? She is in Texas, south Texas.

Thanks


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## Done That (Apr 28, 2011)

Digital:

Demand defrost is more valuable when you see significant amounts of run time below ~ 15-20 degrees F. 

Reason being as outdoor temp drops so does humidity, and therefore less frosting of the coil tends to occur. In this case a Timed defrost system will often sense that the coil is cold and initiate a defrost. Demand system will know that although the coil is cold it is not frosted over, and will delay defrosting. That's kind of the simple explanation. 

In defrost mode the system will energize the electric strip heat to temper the air. So the less often you have to defrost (basically running in AC mode) the less often you use the strip heat and that is where the energy $ savings come from.


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## Bob Sanders (Nov 10, 2013)

user_12345a said:


> Would it make sense to find another two-stage heatpump demand defrost board for another manufacturer's heatpump and rig it up?


Well I was thinking of using that white rodgers single stage board (replacement for older rheem) mentioned in a previous thread here and just adding a relay for the second stage, but I honestly haven't decided if I'm going to use temperature to trigger a defrost, or differential pressure on either side of the coil. Trying to figure out which one is a better deal.



> It would obviously have to support reversing valve energized in cool mode and the same type of condenser fan motor. Some of the higher end 2-speed heatpumps may have a ecm condenser fan motor rather than two speed.


Thank you. That's an excellent point that I never thought of. Mine may well be ECM. It starts fairly slow and winds up over about ten seconds. I'll have to check that.


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## Bob Sanders (Nov 10, 2013)

Bob Sanders said:


> Thank you. That's an excellent point that I never thought of. Mine may well be ECM. It starts fairly slow and winds up over about ten seconds. I'll have to check that.


Just checked it. By the wiring diagram it looks to be a simple multi speed


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## Done That (Apr 28, 2011)

Bob,

Can you post your model number, and even better a picture of the existing control setup?


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## WyrTwister (Jul 22, 2013)

I do not know much about heat pumps , but here goes .

If the condenser coil freezes up , that would diminish air flow , wouldn't it ? Could you control defrost , based on air flow ?

God bless
Wyr


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## Done That (Apr 28, 2011)

Wyr:

Pressure switches, looking at air flow change, were used in the past on some Demand systems. They were a bit expensive, and subject to issues like insects etc "clogging" them. A lot of different methods were tried, often because Mfgs were trying to work around existing patents.

Today all of the Demand systems on air source spits use two thermistors, one on the coil and one measuring outdoor air temp. Thermistors are pretty cheap, and the algorithms behind them have been fine tuned over the years and do a pretty good job.

Higher end and communicating systems utilizing ECM motor feedback and current sensor data probably offer some opportunities to further improve Demand defrost, but right now OEM's are kind of in a "it's not broke, so don't fix it" mode.

BTW, I enjoy your many helpful posts here!


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## WyrTwister (Jul 22, 2013)

Thanks for the complement . 

We live in a pretty dry climate , so de-humidification is not an over whelming issue . 

Likewise I am guessing , HP defrost is not as big an issue as it would be in some areas . But I have seen some units freeze into a " glacier " of ice . :-(

If there were such a thing as average conditions , at what Outside Air Temperature does defrosting become needed ?

I have quoted quite a few HP retrofit where the available electrical was limited & I had to get a commitment from the HVAC contractor that the electric resistance heat would NEVER be on at the same time as the compressor / compressors . 

This approach is probably not optimal . But some times you must work with the existing conditions .

Do not know how he would accomplish that . Never really thought about it that much . Suppose you could do it with an ice cube relay .

These retrofits were often driven by the desire to minimize the electrical consumption of the resistance heat strips .

I once priced a situation at an apartment complex , that had a chill water system . And maybe a boiler , can not remember . 

The underground piping was shot & I think the chillers were , also .

The idea was to abandon the whole system and install HP's for each apartment . 

Each apartment only had a small loadcenter of very limited ampacity . It was very challenging to come up with a workable approach . Privately , I was glad we did not get the project .

Anyway , back to defrost . 

Another idea would be a digital camera focused on the condenser coil with AI software analyzing the image . When sufficient frost build up is observed , defrost is triggered . When the frost was gone , defrost would be shut off ( maybe with a little more time to " dry " the coil ) .

The hardware is not that $$$ . The software may be an issue . But who knows , in the future .

God bless
Wyr


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## Bob Sanders (Nov 10, 2013)

WyrTwister said:


> I do not know much about heat pumps , but here goes .
> 
> If the condenser coil freezes up , that would diminish air flow , wouldn't it ? Could you control defrost , based on air flow ?
> 
> ...


Yes. That's what I was mentioning above. Two ways you can do it; differential temperature, or differential pressure. Can't decide which is better. Leaning towards temperature because unless you go with a more complicated electronic pressure sensor, you have to rely on a mechanical sensor which includes a rubber diaphram (rubber gets stiffer in the cold).


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## Bob Sanders (Nov 10, 2013)

Done That said:


> Bob,
> 
> Can you post your model number, and even better a picture of the existing control setup?


Goodman DSZC160481

http://www.alpinehomeair.com/viewproduct.cfm?productID=453062630


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## Done That (Apr 28, 2011)

Bob,

That's about as complex a control board as you'll find. A few things to consider as you plot to replace it:

1. It can support EITHER a 2-speed PSC or ECM fan, depending on how it's wired. You'll have to keep digging in to make sure on this one.
2. It has an integrated contactor, so you'll have to add a contactor if you use any other control board
3. It has a relay controlling the crankcase heater around ambient temperature
4. You'll have to come up with an output to drive the second stage compressor solenoid
5. Control board has inputs and monitors both the high and low pressure switches during very specific running and temperature conditions
6. Control board has current sensors for faults and protection of the scroll compressor

Can it all be replaced and "upgraded"? Sure, but this is a much bigger project than the other thread that was dealing with a basic 1-stage unit with PSC fan motor.

Hey, this is a DIY site, I'm not saying don't try if you feel like it. Just know that it's a very complex undertaking and the cost to do it may well take many years to recover.


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## user_12345a (Nov 23, 2014)

For the second stage compressor, can't Y2 go straight to the scroll's second stage solenoid?

Low and high pressure switches can be done in series with the contactor's coil, no?


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## Bob Sanders (Nov 10, 2013)

Done That said:


> Hey, this is a DIY site, I'm not saying don't try if you feel like it. Just know that it's a very complex undertaking and the cost to do it may well take many years to recover.


Thanks for the input.
Right now I'm just playing with the idea, and it may not even be needed. The board can adjust for up to 120 minutes defrost time so I think the best thing is to simply operate it as-is for this first year and see how much time it spends defrosting. If it's going to need defrosting every 2 hours or less for the majority of time anyway then there is no sense worrying about it. Demand defrost isn't going to save that much money.


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## Done That (Apr 28, 2011)

user_12345a said:


> For the second stage compressor, can't Y2 go straight to the scroll's second stage solenoid?
> 
> Low and high pressure switches can be done in series with the contactor's coil, no?


When there is a Y2 demand the compressor will need to see it, as will the OD fan motor. Some Copeland scrolls take a direct, un-modulated AC input, others have an in-line DC rectifier and use a pulsed signal. As long as you know what you have.

Sure, pressure switches can be wired in series with the contactor. All I was saying is the control board has times when it does not "look" at the pressure switch...for example during certain defrost conditions. This is to avoid nuisance trips. Certain low ambient conditions as well. This logic would all be lost.


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## zappa (Nov 25, 2011)

Bob Sanders said:


> Thanks for the input.
> Right now I'm just playing with the idea, and it may not even be needed. The board can adjust for up to 120 minutes defrost time so I think the best thing is to simply operate it as-is for this first year and see how much time it spends defrosting. If it's going to need defrosting every 2 hours or less for the majority of time anyway then there is no sense worrying about it. Demand defrost isn't going to save that much money.


The conditions most needed for defrost is about 30 thru 45F with rain/snow/humidity. Mine will ice up during these times when set to 90 minutes but 60 minutes will keep it clear. I set it back to 90 though because of the needless low temperature defrost cycles and higher electric bill.


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## Bob Sanders (Nov 10, 2013)

zappa said:


> The conditions most needed for defrost is about 30 thru 45F with rain/snow/humidity. Mine will ice up during these times when set to 90 minutes but 60 minutes will keep it clear. I set it back to 90 though because of the needless low temperature defrost cycles and higher electric bill.


Yeah... and if it wasn't such a pain changing the timings then I would just leave it at that. You have to take the access plate off and flip a set of PCB mounted mini DIP switches. I may try just replacing the DIP's with a couple of normal sized toggle switches and fixing them somewhere on the outside.


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## user_12345a (Nov 23, 2014)

Done That said:


> When there is a Y2 demand the compressor will need to see it, as will the OD fan motor. Some Copeland scrolls take a direct, un-modulated AC input, others have an in-line DC rectifier and use a pulsed signal. As long as you know what you have.
> 
> Sure, pressure switches can be wired in series with the contactor. All I was saying is the control board has times when it does not "look" at the pressure switch...for example during certain defrost conditions. This is to avoid nuisance trips. Certain low ambient conditions as well. This logic would all be lost.


Sounds like some of these two speed heatpumps are as complex as the high end modulating furnaces.

They sound like more trouble than they're worth, and likely very expensive to repair. I wouldn't be surprised if the control board alone for this goodman was $400.

It's probably best to just leave existing board as is.


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## zappa (Nov 25, 2011)

Nevermind


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## Bob Sanders (Nov 10, 2013)

user_12345a said:


> Sounds like some of these two speed heatpumps are as complex as the high end modulating furnaces.
> 
> They sound like more trouble than they're worth, and likely very expensive to repair. I wouldn't be surprised if the control board alone for this goodman was $400.


Repair clinic is listing them for $271, but yeah, this thing even has the comfortnet communication system on it, which I don't use at all.


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## Bob Sanders (Nov 10, 2013)

I've been reading up on this new "timed" control board Goodman is using. Apparently I may be looking at nothing more than splitting hairs by changing this board over to demand.

The board is time dependent but there is an on-board temp sensor which measures ambient temp. The defrost cycle is locked out until a certain temp. I think it was 28 degrees... or something like that. The time is also based on run time and not clock time so if you set it for 2 hours then it has to RUN for a total of 2 hours before a defrost cycle kicks in. I thought it was clock time and it defrosted every two hours regardless.

If this is all true then I don't see demand defrost saving all that much more money.


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## zappa (Nov 25, 2011)

You may have something there. It's always measured in run time BTW. I still have too many unneeded cycles at the higher temps also. I think mine stops defrosting around ~50F.


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## Bob Sanders (Nov 10, 2013)

Indeed if I look at the wiring diagram there is an outdoor temp sensor as well as a coil temp sensor.

I know that the coil temp sensor has something to do with controlling the length the defrost cycle because there is a dip switch to select the temp (50* or 70*) at which the defrost cycle ends.... but it may be double acting and monitoring the coil temp prior to defrost as well. I've read some other threads in other places and other seem to think that the timer is more about triggering a "CHECK" for frost build up. That's 3rd party guessing though.

This board may be quite a bit more sophisticated than I thought it was.


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## zappa (Nov 25, 2011)

Yeah, my coil Klixon opens at 50F and closes at 32F so if the coil gets cold enough to close it, the defrost cycles will continue. I would think there should be times that defrost is needed below 28?? Does your board also cycle a defrost every 8 hours or whatever for oil return?


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## Bob Sanders (Nov 10, 2013)

Crap.
When in doubt.... read the instructions. :whistling2: 


> DEFROST CONTROL
> During operation the power to the circuit board is controlled by a temperature sensor, which is clamped to a feeder tube entering the outdoor coil. Defrost timing periods of 30, 60 and 90 minutes may be selected by setting the circuit board jumper to 30, 60 and 90 respectively. Accumulation of time for the timing period selected starts when the sensor closes (approximately 34°F), and when the wall thermostat calls for heat. At the end of the timing period, the unit’s defrost cycle will be initiated provided the sensor remains closed. When the sensor opens (approximately 60°F), the defrost cycle is terminated and the timing period is reset. If the defrost cycle is not terminated due to the sensor temperature, a twelve minute override interrupts the unit’s defrost period.


It also goes on to state that a defrost sequence usually lasts for around 3 minutes... which is nothing.
At any rate the coil sensor does have the ability to override and reset the timer if the coil for some reason should go up in temp during a normal run.

If everything works out here as Goodman claims... I don't see demand defrost saving much money


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## zappa (Nov 25, 2011)

That's nothing more than a crappy old timed defrost.


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## yuri (Nov 29, 2008)

Trane, Carrier , York and Lennox have been making heat pumps for 40 yrs so by now they have figured out the timing method very well. Goodman has very good technology now that they got married to Amana. In the old days Amana was built like a Mercedes. I doubt you can improve on all the research and yrs of real world tweaking they have done so I would use it as is. 

And yeah, it does not defrost every 2 hours like yer fridge.:yes::laughing:


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## Bob Sanders (Nov 10, 2013)

yuri said:


> I doubt you can improve on all the research and yrs of real world tweaking they have done so I would use it as is.


Yeah... It's beginning to sound like demand defrost is going to be more trouble than the nickels and pennies that it MIGHT save.


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## Bob Sanders (Nov 10, 2013)

zappa said:


> Does your board also cycle a defrost every 8 hours or whatever for oil return?


No, It says nothing about that. I've heard that before and it's never made any sense to me anyway. An AC doesn't reverse to return oil so why would a heat pump need to?


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## zappa (Nov 25, 2011)

Bob Sanders said:


> No, It says nothing about that. I've heard that before and it's never made any sense to me anyway. An AC doesn't reverse to return oil so why would a heat pump need to?


Because the cold outdoor coil temps makes the oil thick. It doesn't matter now from the Goodman description. There is no mention of the 28 degree ambient sensor that you said earlier. It's just a plain ole timed defrost like everyone else has.


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## yuri (Nov 29, 2008)

Bob Sanders said:


> Yeah... It's beginning to sound like demand defrost is going to be more trouble than the nickels and pennies that it MIGHT save.


They had demand defrost back in the early 80's when York was still Borg/Warner. Old farts like us may remember that company:laughing:. The pressure sensors would ice up and the tubing cracked yadayadayada.

If you think about the small amount of draft the pressure switch is working with and the varying tiny amount of differential across the coil when icing etc it is very hard to make a pressure switch reliable especially when exposed to the outdoors and moisture and bugs etc. Pressure switches are bad enough indoors so to put it in a machine that vibrates and exposed to large climate changes etc never will work well.


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## Bob Sanders (Nov 10, 2013)

zappa said:


> Because the cold outdoor coil temps makes the oil thick. It doesn't matter now from the Goodman description. There is no mention of the 28 degree ambient sensor that you said earlier. It's just a plain ole timed defrost like everyone else has.


Well, the "28*" remark came from another thread (third hand info) so I would not treat it as cold hard fact, but if you look on the wiring diagram for my HP there are definitely 2 sensors there. One is labeled "OAS" Outdoor ambient and the other is labeled "OCS" (outdoor coil). Indeed you can even see the OAS hanging outside the machine


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## zappa (Nov 25, 2011)

See if you can find out what the OAS does. Could be just a convenient sensor for a thermostat. We don't know if the "heat pump only" remark is just for the bottom sensor or both? My guess is just the bottom sensor so that would be a clue that the OAS is not controlling the defrost cycle in any way.


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## Bob Sanders (Nov 10, 2013)

Okay, first you are correct. The OAS is simply the sensor for the comfortnet thermostat and provides the balance point for the AUX heat.


> S-26 TESTING TEMPERATURE SENSORS
> (COMFORTNET READY MODELS ONLY)
> The ASXC and DSXC ComfortNet ready air conditioner models are factory equipped with an outdoor air temperature (OAT) sensor. The OAT sensor allows the outdoor air temperature to be displayed on the CTK0* thermostat when used with the ASXC and DSXC models.
> The ASZC and DSZC ComfortNet ready heat pump models are equipped with both an outdoor air temperature (OAT) sensor and an outdoor coil temperature (OCT) sensor. The OAT provides the balance point temperature in heat pump systems (air handler w/electric heat + heat pump) and dual fuel systems. The OCT sensor is provides the outdoor coil temperature and is used in determining defrost cycles.


Now having said that, there does see to be a difference between the legacy and systems and the comfortnet defrost system. The comfortnet system has the ability to reset the timer should the coil temp go up above 31*.

Legacy systems:


> Solid State Defrost Control
> During operation the power to the circuit board is controlled by a temperature sensor, which is clamped to a return bend (3/8" coils) or a feeder tube (5 mm coils) entering the outdoor coil. Defrost timing periods of 30, 60, or 90 minutes may be selected by connecting the circuit board jumper to 30, 60, or 90 respectively. Accumulation of time for the timing period selected starts when the sensor closes (approximately 31°
> F), and when the room thermostat calls for heat. At the end of the timing period, the unit’s defrost cycle will be initiated provided the sensor remains closed. When the sensor opens (approximately 75° F), the defrost cycle is terminated and the timing period is reset. If the defrost cycle is not terminated due to the sensor temperature, a ten minute override interrupts the unit’s defrost period. The new upgraded defrost control has a 12 minute override interrupt.


Comfortnet:


> DEFROST CYCLE - COMFORTNETTM MODELS
> The defrosting of the outdoor coil is jointly controlled by the
> UC PCB and the outdoor coil temperature (OCT) sensor.
> The OCT sensor is clamped to a feeder tube entering the outdoor coil. Defrost timing periods of 30, 60, 90 or 120 minutes may be selected via the dipswitch settings on the UC PCB. In a communicating system, the defrost timing periods can also be selected in the communicating thermostat user menu. During operation the microprocessor on the UC *checks* coil temperature via the OCT sensor every 30, 60, 90, or 120 minutes when there is a call for heating. If by the time the microprocessor checks the coil temperature, and it's low enough (approximately 31°F), and if there is a call for heat from the thermostat, the PCB will initiate a defrost. When the microprocessor detects the coil temperature to be high enough (approximately 75 0F), or 10 minutes of maximum defrost cycle time has elapsed, whichever occurs first, the defrost cycle is terminated and the timing period is reset. The field service personnel can also advance a heat pump to the defrost cycle by simultaneously pressing the “TEST” button and the “RECALL” button on the UC board.


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## beenthere (Oct 11, 2008)

Bob Sanders said:


> Crap.
> When in doubt.... read the instructions. :whistling2:
> It also goes on to state that a defrost sequence usually lasts for around 3 minutes... which is nothing.
> At any rate the coil sensor does have the ability to override and reset the timer if the coil for some reason should go up in temp during a normal run.
> ...



Thats the standard method a time and temp defrost control uses. 

On demand saves money at lower temps when there isn't enough moisture in the air to frost up or build up ice on the coil. And when its between 36 and 40 degrees outside, and the sun melts the frost off the coil.


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## yuri (Nov 29, 2008)

beenthere said:


> Thats the standard method a time and temp defrost control uses.
> 
> On demand saves money at lower temps when there isn't enough moisture in the air to frost up or build up ice on the coil. And when its between 36 and 40 degrees outside, and the sun melts the frost off the coil.


Which don't happen a heck of a lot of the time where we are.:no:


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## Bob Sanders (Nov 10, 2013)

yuri said:


> Which don't happen a heck of a lot of the time where we are.:no:


LOL!
I'm just going leave it for this year and see how it acts. My mind is going buggy now anyway from all of this reading/research. There is so much conflicting info floating around out there on the net!

I will say the one thing that does really bother me though is those tiny little drain holes at the bottom of the machine. They don't look like they're going to be all that effective. I do have the machine slanted just a bit for better drainage, but I question how much water is actually going to "drain" at -10


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## zappa (Nov 25, 2011)

Bob Sanders said:


> Okay, first you are correct. The OAS is simply the sensor for the comfortnet thermostat and provides the balance point for the AUX heat.
> 
> 
> Now having said that, there does see to be a difference between the legacy and systems and the comfortnet defrost system. The comfortnet system has the ability to reset the timer should the coil temp go up above 31*.
> ...


They are still describing a standard time/temp defrost for both systems. Just blowing a little smoke for the Comfortnet description.

BTW, which system do you have?


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## beenthere (Oct 11, 2008)

How much moisture is in the air in your area at -10°F. Shouldn't be much moisture at that temp. So not much water to drain.


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## Bob Sanders (Nov 10, 2013)

zappa said:


> They are still describing a standard time/temp defrost for both systems. Just blowing a little smoke for the Comfortnet description.
> 
> BTW, which system do you have?


Comfortnet board but it's connected to the IAQ stat.


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## zappa (Nov 25, 2011)

Bob Sanders said:


> LOL!
> I'm just going leave it for this year and see how it acts. My mind is going buggy now anyway from all of this reading/research. There is so much conflicting info floating around out there on the net!
> 
> I will say the one thing that does really bother me though is those tiny little drain holes at the bottom of the machine. They don't look like they're going to be all that effective. I do have the machine slanted just a bit for better drainage, but I question how much water is actually going to "drain" at -10


There is not much water in frost and pretty much all of it evaporates back into the air.


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## Bob Sanders (Nov 10, 2013)

Just calculated out the defrost cost for a month. Defrosting every 2 hours for an entire month (5 minute defrost time including a 5Kw heat strip) will cost me $17. I'm not even sure that's worth worrying about.


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## zappa (Nov 25, 2011)

beenthere said:


> Thats the standard method a time and temp defrost control uses.
> 
> On demand saves money at lower temps when there isn't enough moisture in the air to frost up or build up ice on the coil. And when its between 36 and 40 degrees outside, and the sun melts the frost off the coil.


My outdoor unit doesn't see much sun. If the defrost time is set for too long the frost builds up so thick that it takes a very long time to clear because it's trying to get rid of it from the inside out. The coil temp will get up to 50* and take it out of defrost but the frost is still solid and not allowing much if any air flow.


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## beenthere (Oct 11, 2008)

Did you include that in 5 minutes of defrost, the heat pump will remove about 2600 BTUs more heat, then a 5 KW heater will put in, so the heat pump will have to run a bit longer to recover the loss.

PS: With only 5KW of aux during defrost. The air temp coming out of the registers will be around 18°F colder then the air entering the return.


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## beenthere (Oct 11, 2008)

zappa said:


> My outdoor unit doesn't see much sun. If the defrost time is set for too long the frost builds up so thick that it takes a very long time to clear because it's trying to get rid of it from the inside out. The coil temp will get up to 50* and take it out of defrost but the frost is still solid and not allowing much if any air flow.


The frost probably melts off when its 38 to 40 outside. As teh heat pump shouldn't have to run for hours on end at those temps.


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## zappa (Nov 25, 2011)

beenthere said:


> Did you include that in 5 minutes of defrost, the heat pump will remove about 2600 BTUs more heat, then a 5 KW heater will put in, so the heat pump will have to run a bit longer to recover the loss.
> 
> PS: With only 5KW of aux during defrost. The air temp coming out of the registers will be around 18°F colder then the air entering the return.


Good points. I recently staged mine from 20K to 10K during defrost. At 10K it just barely holds the supply temps that the pump alone was producing.


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## Bob Sanders (Nov 10, 2013)

beenthere said:


> Did you include that in 5 minutes of defrost, the heat pump will remove about 2600 BTUs more heat, then a 5 KW heater will put in, so the heat pump will have to run a bit longer to recover the loss.


Well, I don't think there is any sense in climbing to that level of detail. My ball park estimate is set at 5 minute defrost time while it could actually be 3 minutes, or a whole ten.

The point is that there will be a loss that is not too significant and that demand defrost will simply make an insignificant number just a bit more insignificant. I dunno... these are all guess at this stage... I'll need the Winter to collect some reasonable data to work from.

Let's not forget... mid december, to mid February I'm pretty much back on resistive heat anyway for the night time MINIMUM


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## zappa (Nov 25, 2011)

I wonder if anyone has experimented with coil color? It would seem easy to fab up a sensor to detect white


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## yuri (Nov 29, 2008)

Gas is cheaper.:yes:

The minimum standard is now 95%. Too bad you pisssed off Centra gas or MB Hydro yrs ago and cannot go back.:whistling2:

I could of sold you a Pulse and side vented it and you would have saved a fortune. They were 94-96% efficient back in the early 80's when I put Mom's in. Saved a FORTUNE over the 30 yrs it ran.

Ah, the road less travelled.


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## Bob Sanders (Nov 10, 2013)

zappa said:


> I wonder if anyone has experimented with coil color? It would seem easy to fab up a sensor to detect white


Interesting concept, although I may dream up a way to fool the coil sensor... I would rather not get rid of the comfortnet board. Maybe a differential pressure sensor connected to a small heating element just big enough to keep the cold off the sensor. The pressure drops due to ice then the element switches off and the sensor cools.... dunno... just playing with ideas right now.


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## beenthere (Oct 11, 2008)

Bob Sanders said:


> Well, I don't think there is any sense in climbing to that level of detail. My ball park estimate is set at 5 minute defrost time while it could actually be 3 minutes, or a whole ten.
> 
> The point is that there will be a loss that is not too significant and that demand defrost will simply make an insignificant number just a bit more insignificant. I dunno... these are all guess at this stage... I'll need the Winter to collect some reasonable data to work from.
> 
> Let's not forget... mid december, to mid February I'm pretty much back on resistive heat anyway for the night time MINIMUM


Short defrost times, and usually only when its not real cold outside.



zappa said:


> I wonder if anyone has experimented with coil color? It would seem easy to fab up a sensor to detect white


Unfortunately, snow is white. Plus, the photo sensor would get dirty and not see the color.


Years ago, Whirlpool used an air pressure sensor, it was very accurate determining when a defrost was needed.


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## Bob Sanders (Nov 10, 2013)

yuri said:


> Gas is cheaper.:yes:
> 
> The minimum standard is now 95%. Too bad you pisssed off Centra gas or MB Hydro yrs ago and cannot go back.:whistling2:
> 
> ...


I can go back to gas anytime... gotta pay the service fees. Don't want gas is the point.


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## Bob Sanders (Nov 10, 2013)

Bob Sanders said:


> Interesting concept, although I may dream up a way to fool the coil sensor... I would rather not get rid of the comfortnet board. Maybe a differential pressure sensor connected to a small heating element just big enough to keep the cold off the sensor. The pressure drops due to ice then the element switches off and the sensor cools.... dunno... just playing with ideas right now.


Actually I should do some research on the coil sensor Goodman is using. If it's simply a temperature sensitive resistor (and they usually are when there are only 2 leads off of it) then it SHOULD be pretty easy to fool the board.

Rig up a differential pressure sensor to a relay which switches in/out a high/low resistance value and replace the sensor with that.


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## zappa (Nov 25, 2011)

beenthere said:


> Unfortunately, snow is white. Plus, the photo sensor would get dirty and not see the color.
> 
> 
> Years ago, Whirlpool used an air pressure sensor, it was very accurate determining when a defrost was needed.


Well, it would be inside very close to a coil tube and shielded from both horizontal and vertical snow. Dirt could be an issue.

In my case, how about a humidistat in series with the coil Klixon? It would simply turn the existing time/temp defrost on only at a set humidity level. Might have to add a timer circuit to do the oil return thingy if it ever went for that long??


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## zappa (Nov 25, 2011)

Bob Sanders said:


> Actually I should do some research on the coil sensor Goodman is using. If it's simply a temperature sensitive resistor (and they usually are when there are only 2 leads off of it) then it SHOULD be pretty easy to fool the board.
> 
> Rig up a differential pressure sensor to a relay which switches in/out a high/low resistance value and replace the sensor with that.


All the ones I have seen are mechanical Klixons.


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## beenthere (Oct 11, 2008)

zappa said:


> Well, it would be inside very close to a coil tube and shielded from both horizontal and vertical snow. Dirt could be an issue.
> 
> In my case, how about a humidistat in series with the coil Klixon? It would simply turn the existing time/temp defrost on only at a set humidity level. Might have to add a timer circuit to do the oil return thingy if it ever went for that long??


Could be a lot of trial and error to get it st up right.


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## zappa (Nov 25, 2011)

beenthere said:


> Could be a lot of trial and error to get it st up right.


The humidistat?


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## Bob Sanders (Nov 10, 2013)

zappa said:


> All the ones I have seen are mechanical Klixons.


Even easier


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## Bob Sanders (Nov 10, 2013)

zappa said:


> In my case, how about a humidistat in series with the coil Klixon? It would simply turn the existing time/temp defrost on only at a set humidity level. Might have to add a timer circuit to do the oil return thingy if it ever went for that long??


If it's just a klixon then I'm thinking the white rodgers demand defrost board mentioned in the other thread with it's relay contact in place of the klixon.

The only complication I can see with that is that there will be a 30 minute time delay before the actual defrost session takes place (30 minutes is the earliest you can set the goodman board of course) so you would need to set the demand defrost sensor in the MOST sensitive part of the coil. (If you read that thread then you will remember the OP had to change the location of his sensor because it wasn't sensitive enough in its original location).

This will allow you to both keep the original board in play and easily reverse things if you don't like the reaction.


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## zappa (Nov 25, 2011)

Bob Sanders said:


> If it's just a klixon then I'm thinking the white rodgers demand defrost board mentioned in the other thread with it's relay contact in place of the klixon.
> 
> The only complication I can see with that is that there will be a 30 minute time delay before the actual defrost session takes place (30 minutes is the earliest you can set the goodman board of course) so you would need to set the demand defrost sensor in the MOST sensitive part of the coil. (If you read that thread then you will remember the OP had to change the location of his sensor because it wasn't sensitive enough in its original location).
> 
> This will allow you to both keep the original board in play and easily reverse things if you don't like the reaction.



I need to read up on how the demand board works again cause I forgot already.  Two sensors, right? But I can't remember what they do. If I bought the demand board there would be no reason to keep mine in place.


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## Bob Sanders (Nov 10, 2013)

Yeah. There is an ambient and a coil sensor and I'm pretty sure the two temps are compared to each other.


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## Bob Sanders (Nov 10, 2013)

zappa said:


> All the ones I have seen are mechanical Klixons.


Apparently the legacy models are klixon.The comfortnet is indeed a thermistor. Fortunately the service manual lists the temperature/resistance values so I won't have to pop the bloody thing in and out of the freezer!


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## beenthere (Oct 11, 2008)

zappa said:


> The humidistat?


Yes. Remember, air at 30°F and 50% RH has 70% more moisture in it then air at 20°F, and 50%RH.


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## zappa (Nov 25, 2011)

beenthere said:


> Yes. Remember, air at 30°F and 50% RH has 70% more moisture in it then air at 20°F, and 50%RH.


Ahhh...gotcha, so if it was always the same temp outside that would be the only way it would be accurate?

I'm finding all kinds of roadblocks (yours is a huge one) now that I'm looking into this. I was originally thinking a simple mechanical band style but they won't work below freezing for obvious reasons. :whistling2:

This would be an option (only $26) but more trouble than it's worth because the box would need to be installed inside a conditioned space for temp and condensation reasons. Interesting though, it has a temperature probe for the exact reason that you mentioned I think. It doesn't display temperature but the info is saying it uses the probe to keep the humidity reading accurate.


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## Bob Sanders (Nov 10, 2013)

So.
Mount the box inside. That's what I did with my external low temp condenser lock out
The box is mounted on the airhandler and I simply extended the probe wire to the outside. (The box on the left is the outdoor temp/condenser lock out)


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## Bob Sanders (Nov 10, 2013)

I'm not sure why you're making things difficult though Zappa. If you're not afraid to replace your board then you should just go the white rodgers demand defrost board It's all there.. temp compensation, settable defrost cycle length, short cycle protection.... etc. It even has a basic fault light



> The 47D40-801 control is a microprocessor-based demand defrost controller intended for Rheem heat pump systems. This controller uses basic differential temperature means to detect degradation of system performance due to ice build-up on the outdoor coil. The controller uses “self-calibrating” principles to calibrate to the heat pump system. The defrosting is performed by reversing the refrigerant direction of ﬂow.





> Each controller has 24 VAC input and B, Y, and D terminals for connection to a standard thermostat. The controller has pins for connection of two temperature sensors to measure ambient and coil temperature. Controlled outputs are outdoor fan, reversing valve, and compressor contactor.


Relatively cheap too.... $55
http://www.amazon.com/White-Rodgers-47D40-801-Demand-Defrost-Control/dp/B006JQ368W

All you need to do is rewire the RV relay

(actually... just found one for $37.62)
http://www.patrickssupply.com/product-p/47d40-801.htm


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## zappa (Nov 25, 2011)

Bob Sanders said:


> I'm not sure why you're making things difficult though Zappa.


I enjoy experimenting with different ways of doing things which often leads to learning, as in this case. I originally thought mechanical band which would have been SUPER easy to install. Now it's not so easy anymore so I'm back to the demand board. While I was searching eBay for humidistats I came across these cool boxes and was amazed at the price. Years ago one would pay a small fortune for a control box like these.

If I'm understanding correctly what beenthere is saying, I think this idea would work very well along with the temperature compensation probe. If I had a new complex unit like yours and didn't want to do any major mods I would experiment with this idea in a heartbeat. Especially for $26 and free shipping. :laughing:


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## Bob Sanders (Nov 10, 2013)

zappa said:


> While I was searching eBay for humidistats I came across these cool boxes and was amazed at the price. Years ago one would pay a small fortune for a control box like these.


They're pretty accurate and run on a wide range of voltages too. I picked up 2 of the temperature ones. They work for switching both heat and refrigeration. They have a settable deadband range between the trigger temp and you can adjust the sensitivities. All that for $13 each!


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## Bob Sanders (Nov 10, 2013)

So, I think I figured out what I'm going to do here. I'll use the White rodgers (rheem) temperature demand defrost board, but I won't replace my comfortnet board with it... it's just too integrated into the system.

The comfortnet board allows you to force a defrost session for testing purposes by pressing the "RECALL" and "TEST" buttons at the same time for about 3 seconds. I'll use one of the relays on the demand defrost board connected to a momentary relay which will simulate a 3 second push on the above mentioned buttons. The coil temp sensor on the comfortnet will be removed and a resistor installed to simulate 60 degrees or so permanently. I will use another relay on the demand defrost board to kick in an appropriate resistor to the comfortnet coil sensor connections to simulate 75 degrees (the temp required for the comfortnet to terminate the defrost session.

I'll have to do some minor mods on the comfortnet board... solder in some wires off the test and recall buttons so I can connect to the relay, but other than that, everything is easily reversible should I not like the results.

The end result however SHOULD be demand defrost which completely side steps the timed/temp on the comfortnet board.


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## Bob Sanders (Nov 10, 2013)

So I did a quick little experiment today on my HP based on the above plan.

I disconnected the coil temp sensor (a simple thermistor) and replaced it with a 27k resistor. That simulates a temp of about 38 degrees. It's not really crucial what I use there... I just don't want the confortnet board to start a defrost countdown which happens at 31 degrees (34k) or below. The other important resistance is 11k which is 75 degrees which triggers a defrost termination. So as long as I stay between 11k and 34k I pretty much mute out any defrost activity from the comfortnet board.

I then started the heat, gave it a few minutes to settle out its pressure, then manually triggered a defrost session by pressing the TEST and RECALL buttons for 3 seconds. The defrost started, heatstrip came on as normal and I let it sit in defrost for a few minutes. Then I paralleled in a 10k resistor over the 27k resistor (10k in parallel with 27k is a little bit under 10k which works out to about 78 degrees... over the 75 degree termination point) and inside of 8 seconds the defrost session ended and it went back into heating mode.

The test was done 3 time just to confirm it works.... and it does... so now it's just a matter of building it all up. I even went and ordered the WR defrost board.

See Yuri... you can't have this kind of fun with a bland and dreary gas furnace


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## Ben25 (Jun 14, 2014)

Looks like fun. I got a mitsubishi hyper heat mini split last year and heated with it over the winter. Only problem was it has a timed defrost every 45 minutes which killed the output. We are a diamond dealer for mitsubishi, so I mentioned it to them, and they sent out a factory tech with a programming tool. He flashed the circuit board (took 4 seconds) and then I had demand defrost. Goes from 45 min to at least 3 hrs now.


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## zappa (Nov 25, 2011)

Did your resistors get too hot and warp the siding?


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## Bob Sanders (Nov 10, 2013)

zappa said:


> Did your resistors get too hot and warp the siding?


LOL!
No. The BBQ did that. That's all new siding too. I wasn't very happy


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## beenthere (Oct 11, 2008)

Its set a bit too close to the house.


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## Bob Sanders (Nov 10, 2013)

beenthere said:


> Its set a bit too close to the house.


It only looks that way from the picture. The actual distance is what was recommended in the install manual.


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## Bob Sanders (Nov 10, 2013)

Got around to taking the comfortnet board out today so I can do the necessary (minor) mod on it. Soldered my leads onto the board over the TEST and RECALL buttons. Both buttons are common to ground so I only needed three wires out of it to connect to the defrost board.





















The buttons require a simultaneous push and hold for about 2 or 3 seconds and then release. The WR defrost board however puts out a constant voltage from start of defrost to finish so I will have to build a momentary relay which will take the constant voltage delivered from the defrost board and turn that into a pulse about 2 or 3 seconds long. The below configuration will take care of that. The relay closes until the cap is charged at which point the current drops off and the relay opens. Timing is set by the size of the cap. This one is about 1/2 a second so I'll need at least 3000uf, maybe just a bit more... I'll have to experiment.


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## WyrTwister (Jul 22, 2013)

Consider using an adjustable time delay relay .

What does it do if it is given a long cloaure ?

God bless
Wyr


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## Bob Sanders (Nov 10, 2013)

WyrTwister said:


> Consider using an adjustable time delay relay


Time delay relay isn't quite the same. As far as I know it closes AFTER a preset time, and is not momentary. I need quite the opposite. I need it to close right away and to stay closed for no more than about 3 seconds. The above circuit will do that, and it's cheap (already have the parts).

I actually used this relay design a while back on an old motor. The centrifugal switch burned out and I couldn't get parts so I used this relay to set up for about a 3/4 second bounce to kick in/out the start winding.



> What does it do if it is given a long cloaure ?


I've held it as short as 1 and as long as 4 seconds. One second is kind of iffy... sometimes it works and sometimes it doesn't. I didn't go any further than that though... there is no sense, but clearly the buttons need to be pressed AND released before the defrost session starts.


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## Ben25 (Jun 14, 2014)

A single shot relay may work for you.


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## Bob Sanders (Nov 10, 2013)

Ben25 said:


> A single shot relay may work for you.


Well that's basically what the above circuit is... one shot with a 3 second closing..... only at about 1/3 the price.

When you supply power to the relay the contacts close for the predetermined time (set by the size of the cap), then they open. They do not close again until power is disconnected, then reconnected (or in other words, till the next defrost session)


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## Ben25 (Jun 14, 2014)

I see. Must have not read correctly and thought you were still looking for something to do that.


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## WyrTwister (Jul 22, 2013)

There are all different kinds of time delay relays .

But , if you alreadr have the parts to build what you need .........

God bless
wyr


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## Bob Sanders (Nov 10, 2013)

Started building up my board. It's pretty simple... and looks pretty empty without the other parts (coming in the mail) but what I have now is a momentary relay set for about 2.5 seconds (that took a 1500u cap) and the resistor network which will be used to fool the coil temp sensor electronics on the comfortnet board.










The coil temp sensor (thermistor) will be permanently disconnected from the board and resistors 1,2 will go in its place (didn't have the exact resistor value I wanted so I just ran 2 series to make up the number I was comfortable with). These resistors will permanently report the coil temp as being roughly 42 degrees. That's over the trigger temp (31 degrees) so a defrost timing sequence on the comfortnet board should be effectively killed. The ACTUAL reporting temp however under normal conditions will be about 80 degrees because under normal conditions R3 will be running in parallel with R1,2 and will be switched out during defrost.

On the comfortnet board the defrost is terminated when the coil temp sensor sense 75 degrees. Given that, R3 will be connected to a normally closed contact on the white Rodgers defrost board. When the WR board triggers a defrost that contact will open and remove R3 from the circuit. The reported temperature will now be below 77 degrees (but still above 31 so a confortnet timing sequence will not happen).

When the white Rodgers board is finished defrosting, the R3 relay contact will go back to normally closed and thereby reinserting R3 back into the circuit which will then report the temp as being above 75 degrees and the comfortnet board will terminate the defrost session.

Now there was a concern on initial testing as to whether or not the comfortnet board was sophisticated enough to recognize a 'jump' from one temp to the next as opposed to a gentle rate of rise/drop and throw an error code. Fortunately it is not. It only cares about the trigger temps.

R4 is simply a bleed resistor which bleeds out the charge on the cap so it can get ready for the next defrost session.

Connector 5 will go to the comfortnet coil sensor connector

Conector 6 is where my modded comfortnet connection will fit.

Just for the heck of it I did check out commercially built time delay relays, and it certainly would be easier using one since I can find them at 24vac (My home made relay operates on 12vdc so I have to use a converter from 24vac to 12vdc... which is in the mail.... cheaper to buy than build... $5 plus shipping), but all I could find (at some kind of reasonable price) was 'delay before closing' and I need a delay to open AFTER closing. Now that's not the end of the world.... I would simply use the normally closed contact so when the relay energizes after 2 seconds it removes power (effectively the same as a 'delay to open after closing), but then it's not fail safe. If for some reason the relay fails it will of course fail normally closed which would deliver a constant and endless 'pressing action' on the TEST and RECALL buttons. I did not test for that and don't know how the board will react... but it can't be good!


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## Bob Sanders (Nov 10, 2013)

Well, here's the finished product. It's been bench tested and does work. Have yet to test it for real though. Need some cooler weather for that. I fear it's coming.










The WR defrost board (actually a rheem board) is just mounted on top of my pc board as is the 24vac to 12 dvc converter. It was cheaper to buy one than build.

I still have to mount a relay to reverse the reversing valve issue. The B connection on the rheem defrost board wants 24 volts to know the system is in heating mode which comes from the reversing valve. Of course the goodman delivers 24 volts during cool mode, not heating mode. I may use one of the unused relays on the defrost board or add another one which ever is simpler


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## beenthere (Oct 11, 2008)

The B terminal of a Rheem/Ruud board does not get its 24 volts from the RV. It gets it from the stat on a heating call.


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## Bob Sanders (Nov 10, 2013)

beenthere said:


> The B terminal of a Rheem/Ruud board does not get its 24 volts from the RV. It gets it from the stat on a heating call.


Thanks.
It may be six to one or half a dozen to the other, but the defrost board schematic shows B going to the reversing valve. The B however does not go directly through to the reversing valve as indicated though. There is a sensor on the board which senses whether or not 24 volts is running through. If not then defrost is disabled.

Either way though .... it need 24 volts in heating mode and my RV gives 24 when cooling so it will need to be reversed.


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## beenthere (Oct 11, 2008)

The RV is not a power controlling device. It is controlled by power. 24 volts is sent to the B terminal to put it in heating mode(Rheem/Ruud). When the NC contact on the board opens, it is in defrost mode, and no power is sent to the RV's coil. 

A small relay wired in between the board and RV's coil, so that the relay's contacts open when energized during a heat call will work. You just have to set your stat to energize in heat mode.


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## Bob Sanders (Nov 10, 2013)

beenthere said:


> The RV is not a power controlling device.


Well, I never said that and if I gave you that impression then my writing is not clear and I apologize. The power is coming from the rv CIRCUIT and is being monitored by the board.

The board is using the signal sent to B to tell whether or not the system is in heating mode. If there is no 24 volts then the board figures you're in cooling mode and disables defrost so you don't get defrost sessions during the summer.

I'll be using the same signal from my goodman rv circuit, but it is reversed so I will have to turn that around with a relay to give 24vac while in heat mode.


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## zappa (Nov 25, 2011)

You may be able to use the existing relay on the board as I notice that the NO contact is not being used (pic post #17 in the other thread).

Break the trace going to NC and jump it to NO. He has also opened a small trace going to common (and B) but didn't mention where it goes. If that is the voltage sense circuit leave it connected. If not, you may have to break the sense circuit and wire it directly to the B signal from your stat.


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## Bob Sanders (Nov 10, 2013)

Well, installed the board this morning and tested it. It most definitely does work when I place the rheem board into defrost mode. When I turn on the rheem test switch the condenser does go into defrost mode and kicks back into normal mode when the rheem test switch is turned off. Now I have to wait until cold weather to confirm it all works, but I don't see any reason why there would be complications.

I have set the rjeem board up so that the defrost session ends when the coil temp hits 50 degrees as opposed to its highest setting (80 degrees) My reasoning is that I want defrost cycle to be short (it may come on a bit more often though) so that I MIGHT be able to get away with a 5kw heat strip for defrost heat makeup. It takes almost 3 minutes for defrosts sessions to start blowing really cold, uncomfortable air so HOPEFULLY provided I can get a defrost cycle short enough a 5Kw coil will only be needed. After 3 minutes or so though all bets are off and I'm looking at 10kw of heat strip to do the job. We'll see how that turns out when the time comes.

I did add an additional relay as noted above to reverse the required output from the RV circuit and that worked out fine. The only other thing I did was use one of the other spare relay contacts to run an event counter so I can keep track of how often it goes into defrost.

I did wrap a piece of foam around the rheem coil sensor to better insulate from ambient temperature. Don't know if that was such a smart idea. I have never seen it done on commercial sensor installs, but it just makes more sense to me that the coil sensor needs to sense coil as much as possible and ambient temp as little as possible. We'll see... I may be kicking myself in the butt for that and opening it up later to remove it.



















On a side note, while I had the condenser open I saw something that did NOT make me happy. A couple of the coil tubes were dented in. I looked around for anything even remotely close by which could do such a thing, and found nothing so clearly it was done at the factory during install or handling. I tested with soapy water and there are no leaks... but it's still a bit of a piss off to see that!


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## Bob Sanders (Nov 10, 2013)

Well, it's the first 32 degree day we have had so far. No defrost cycles yet. In fact haven't seen any frost at all forming so I don't really expect to get anything more than a single defrost cycle ever 6 hours (oil return).

It's still operating in single stage mode. Haven't seen a second stage yet. Output temp is a pretty respectable 104 degrees. It's doing about 2 or 3 cycles an hour... maybe about 8 or 10 minutes each time.

No complaints as of yet.


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## beenthere (Oct 11, 2008)

Might want to pull up the performance specs for it. I think your heat pump is only suppose to have a 20 to 22°F temp rise at 30°F. So unless your house is at 80 to 82°F, you may have a very low air flow.

Or a strip heater is coming on when it shouldn't.


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## Bob Sanders (Nov 10, 2013)

beenthere said:


> Might want to pull up the performance specs for it. I think your heat pump is only suppose to have a 20 to 22°F temp rise at 30°F. So unless your house is at 80 to 82°F, you may have a very low air flow.
> 
> Or a strip heater is coming on when it shouldn't.


heat strips are locked out until 10 degrees. House is 71. CFM on 1st stage is 1000... should be 1100 but i don't like hearing it.


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## beenthere (Oct 11, 2008)

Well, then at a 33°F temp rise. Your only moving 810CFM give or take a few CFM.


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## Bob Sanders (Nov 10, 2013)

beenthere said:


> Your only moving 810CFM give or take a few CFM.


I suppose it's possible, but the blinking cfm indicator light says 1000


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## beenthere (Oct 11, 2008)

The blinking indicator only blinks what it is set for. Not what its delivering.

1000 CFM at a 33°F temp rise would be 35,640 BTUs. Your heat pump doesn't have that ability/capacity in first stage at 35°F, let alone at 32°F. So it can't be moving 1000 CFM. Unless a strip heater is coming on also. 

Might want to put an amp probe on and verify that one isn't coming on.


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## Bob Sanders (Nov 10, 2013)

beenthere said:


> Unless a strip heater is coming on also.
> 
> .


As already stated the back up heat is (confirmed) locked out


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## user_12345a (Nov 23, 2014)

How far can the actual cfm deviate from the set cfm?

I would think it would be fairly close until you hit around 0.8"+, especially a 4 ton air handler pushing 1000 cfm when it's capable of much more.

Could have uneven heat coming off the coil; meaning one side is hotter than the other.


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## beenthere (Oct 11, 2008)

Bob Sanders said:


> As already stated the back up heat is (confirmed) locked out


You may have it set to be locked out. But something may not be functioning right. 



user_12345a said:


> How far can the actual cfm deviate from the set cfm?
> 
> Varies with manufacturer, and their module programming.
> 
> ...


12°F hotter then it should be, would indicate a coil with a circuit problem.


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## Bob Sanders (Nov 10, 2013)

It's a bit warmer out today so it's hard to tell but I'm thinking I made a mistake yesterday in converting C to F (I do that on boards because most Americans don't understand what a C is)

But today it's a bit warmer out and this is what I have: (1st stage only)










As already stated, heat strips are CONFIRMED locked out.


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## beenthere (Oct 11, 2008)

I've seen heat strips that were locked out by the stat, still produce heat. Because a piece of sheet metal cuttings fell against then and shorted out to the metal frame, and produced enough heat that the A/C couldn't cool the home when it was 90 outside, but could when it was 85 outside. Jut something to keep in mind.

Of course, if the heat strip isn't producing any heat, then your not moving 1,000 CFM. And should check your total static pressure.


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## Bob Sanders (Nov 10, 2013)

Well, today we have had our first 5 degree F day (-15C)... it's been kind of warm this year (global warming I guess  )

A few things to report.....
I'm not wild about the rheem defrost system. I think it works ok when the temp hovers around 32F. There is quite a bit of humidity and the system need to defrost often. The rheem defrost system seems to get a little confused at 32F. I'm not sure how they work out a defrost by comparing the ambient temp and the coil temp but right at 32F ambient, it sometimes can't make up its mind if a defrost should take place or not so there are days when it is defrosting when it doesn't really have to and other days when it's pretty thick with frost and should have defrosted some time ago.

Above 32F the rheem system does have the ABILITY to save a few bucks, but I emphasize 'ability' because the goodman system can pretty much match it as long as you adjust the defrost timing accordingly (which takes all of a minute or two to change)

Once you start hitting about 12F though it really doesn't make much difference which system you use. There is not much humidity and defrosting can be put off for much longer times. Meanwhile the rheem defrosts once every 6 hours or so (clock time) whether it needs it or not to return oil to the compressor, and with the goodman set at 120 minutes (running time) a defrost won't take place for 4 to 6 hours anyway depending on your duty cycle at a given temperature.

I may experiment next season with defrosting via pressure differential because that (in theory anyway) would seem to be the most accurate way to go. If the coil plugs up with frost pressure in the casing drops. If there is no (or little) frost there the pressure doesn't drop.

The over sizing of the HP seems to have worked out well (4 ton in place of 2 ton). Last night was the first night I had to use stage 2 on the machine and at 5F ambient I'm now getting a duty cycle of 12 minutes on, 12 minutes off with a duct outlet temp of about 88F so clearly I still have a bit to go before I bottom out with the HP. I'm thinking I should be able to get to at least -5F with no back up heat. (I have not had to use the backup heat at all yet and yes BT... that has been confirmed  )

I'm not wild about the staging control. Normally you start up on stage 1 and only go to stage 2 when it becomes clear to the thermostat that stage 1 isn't cutting it. This can lead to really long stage 1 running times before stage 2 kicks in which adds a lot of unnecessary wear and tear to the compressor. I have manually bypassed stage one and it starts/finishes in 2 now which drastically shortens running time. I have another thermostat control on order and when it comes I'll set it up so that stage 1 is automatically bypassed at a set temperature.

The electrical saving has been good compared to my old resistive heat. The October bill was 571Kw cheaper than last year and the November bill is looking like it will be 1217Kw less.


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## beenthere (Oct 11, 2008)

They are suppose to run in first stage most of the time. Hard wear and tear on the compressor is from starting and stopping. 

Read the below article on Snowball. It ran non stop for 28 years.

https://www.trane.com/residential/en/why-us/testing-facility.html


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## beenthere (Oct 11, 2008)

Bob Sanders said:


> The electrical saving has been good compared to my old resistive heat. The October bill was 571Kw cheaper than last year and the November bill is looking like it will be 1217Kw less.


What where the heating degree days for last year's October and November in your area.


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## zappa (Nov 25, 2011)

beenthere said:


> They are suppose to run in first stage most of the time. Hard wear and tear on the compressor is from starting and stopping.
> 
> Read the below article on Snowball. It ran non stop for 28 years.
> 
> https://www.trane.com/residential/en/why-us/testing-facility.html


And that's why I don't want my heat pump starting and stopping 2 extra times during each defrost cycle.


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## Bob Sanders (Nov 10, 2013)

beenthere said:


> They are suppose to run in first stage most of the time. Hard wear and tear on the compressor is from starting and stopping.
> 
> Read the below article on Snowball. It ran non stop for 28 years.
> 
> https://www.trane.com/residential/en/why-us/testing-facility.html


Interesting. I guess it's just me. It seems to go against my grain to see something running for hours on end when it doesn't have to.


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## Bob Sanders (Nov 10, 2013)

beenthere said:


> What where the heating degree days for last year's October and November in your area.


We were above seasonal norms:
http://www.accuweather.com/en/ca/winnipeg/r3b/october-weather/48989

According to our POCO this year the average for October was 9.8C compared to 9.4C last year


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## beenthere (Oct 11, 2008)

Like a car engine. Starting it is the hardest thing to do to it under normal operation.


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## beenthere (Oct 11, 2008)

Wunder Ground Weather

Shows last October had some colder days then list year. Along with a good number that were warmer. 

The above site is a good one to track from year to year.


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## Bob Sanders (Nov 10, 2013)

zappa said:


> And that's why I don't want my heat pump starting and stopping 2 extra times during each defrost cycle.


Speaking of defrost... one other thing I plan to correct. Defrost only works during heat demand so if you have a defrost happening when a heat demand stops, the defrost stops 1/2 way through too. Of course it picks up again where it left off on the next heat demand, but it drives me crazy. I may add relay to lock the system on until the defrost cycle finishes.


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## Bob Sanders (Nov 10, 2013)

beenthere said:


> Wunder Ground Weather
> 
> Shows last October had some colder days then list year. Along with a good number that were warmer.
> 
> The above site is a good one to track from year to year.


I don't remember when we actually started the heat but I do know that October was not a full month of heat. I think it wasn't until the end of the first week of October that we actually turned it on.


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## user_12345a (Nov 23, 2014)

Bob Sanders said:


> Interesting. I guess it's just me. It seems to go against my grain to see something running for hours on end when it doesn't have to.


That's the reason to have two-stage or modulating equipment in the first place; runs constant. That's what they do with centrifugal chillers too; there's a capacity control and it just runs constant until the load falls below the minimum capacity.

A shame that most residential equipment can be so oversized that low matches capacity at design temp.

The continuous operation is also much more comfortable.


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## WyrTwister (Jul 22, 2013)

I read that part of the start up wear for car engines is because o fpoor lubrication until the engine gets up to " normal " operating temperature .

Is it the same with refrigeration / HVAC compressors ?

How does compressor life ( in years ) compare between hheat pumps and straight A/C ?

God bless
Wyr


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## user_12345a (Nov 23, 2014)

...no idea; i think heatpump compressors would have shorter lives because of the defrost cycles and starts in cold weather. I'm sure run-time is important; ie bearing life. The heatpumps have crank-case heaters on them which must help with the lubrication on cold startup..


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## beenthere (Oct 11, 2008)

CCH helps to keep the liquid refrigerant out of it.

The start windings in a compressor are very thing, and can fail due to heat from starting the compressor. Specially if they start up against a pressure difference.


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## user_12345a (Nov 23, 2014)

...so do hard start kits increase or decrease the life of the start winding? presumably they raise current, not just shift the phase.


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## WyrTwister (Jul 22, 2013)

Head pressure

I use and highly recommend time delay relays on the 24 VAC condenser start circuit . To minimize starting against high head pressure .

God bless
Wyr


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## Bob Sanders (Nov 10, 2013)

WyrTwister said:


> Head pressure
> 
> I use and highly recommend time delay relays on the 24 VAC condenser start circuit . To minimize starting against high head pressure .
> 
> ...


I would think head pressure would be more a worry in the summer than winter. I know hard start caps are recommended in high heat areas because of the increased head

I worry about pressure becoming too low in the cold. I don't think you get high head with defrost either. At least not with goodman... the rv equalizes pressure when it reverses plus there is a 30 second delay before it starts again for defrost.


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## zappa (Nov 25, 2011)

Bob Sanders said:


> I would think head pressure would be more a worry in the summer than winter. I know hard start caps are recommended in high heat areas because of the increased head
> 
> I worry about pressure becoming too low in the cold. I don't think you get high head with defrost either. At least not with goodman... the rv equalizes pressure when it reverses plus there is a 30 second delay before it starts again for defrost.


There are some TXV systems that don't equalize. Higher efficiency in less time.


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## beenthere (Oct 11, 2008)

user_12345a said:


> ...so do hard start kits increase or decrease the life of the start winding? presumably they raise current, not just shift the phase.


Help. They get the motor moving faster so the start windings are in the circuit for a shorter period of time.



WyrTwister said:


> Head pressure
> 
> I use and highly recommend time delay relays on the 24 VAC condenser start circuit . To minimize starting against high head pressure .
> 
> ...


Balance port TXVs maintain high head pressure for several hours. So adding an additional 5 mntes delay to a heat pump compressor won't help any thing.


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## beenthere (Oct 11, 2008)

Bob Sanders said:


> Once you start hitting about 12F though it really doesn't make much difference which system you use. There is not much humidity and defrosting can be put off for much longer times. Meanwhile the rheem defrosts once every 6 hours or so (clock time) whether it needs it or not to return oil to the compressor, and with the goodman set at 120 minutes (running time) a defrost won't take place for 4 to 6 hours anyway depending on your duty cycle at a given temperature.
> 
> Your Rheem on demand is 6 hours of accumulated compressor run time. Since it can't bring on the system itself to do a defrost.
> 
> ...


So you keep your place at 73°F. At 5°F it should only be doing a 15°F delta.


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## Bob Sanders (Nov 10, 2013)

beenthere said:


> So you keep your place at 73°F. At 5°F it should only be doing a 15°F delta.


I keep the place at 70... about that anyway


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## user_12345a (Nov 23, 2014)

What size and type of house do you have?

It can't be needing much heat if even an oversized heatpump is keeping up at that outdoor temp.


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## Bob Sanders (Nov 10, 2013)

user_12345a said:


> What size and type of house do you have?
> 
> It can't be needing much heat if even an oversized heatpump is keeping up at that outdoor temp.


It's 103 years old, lath and plaster, about 1500Sq ft, 2 floors with basement (heated). It's been re-sided with added 2 inch Styrofoam insulation on the outside though.

It's -10c (14F) right now and the HP is working on stage 1 and even with that it's not constant and cycling a bit. Defrosting (at the moment) is required about every 4 to 5 hours.

My November electric bill is going to be about 1566Kw. About 1000 of that is normal electrical use so heat for November (actually it's Oct 21 to Nov 21.... don't ask me why they bill that way) is (ball park) 566Kw
With our electric rates that's about 40 bucks.


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## WyrTwister (Jul 22, 2013)

Sorry , you are probably correct . My mind set is A/C .

But I would not think it would not hurt anything , even on a heat pump in winter ?

Does the RV cycle every time the condenser gets a call for heat ? I have read it is actually move / bushed via high pressure gas , that is controlled by a little electric solenoid .

Does it spring return to the A/C position ?

Thanks ,
Wyr
God bless


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## beenthere (Oct 11, 2008)

WyrTwister said:


> Sorry , you are probably correct . My mind set is A/C .
> 
> But I would not think it would not hurt anything , even on a heat pump in winter ?
> 
> ...


No spring load on RVs. They don't cycle everytime, except for on some older thermostats.

A scroll compressor starts unloaded. That is why they don't require hard start kits when they are in TXV systems. But they are not always off of the stat winding when they load. So starting is still hard on them.


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## Bob Sanders (Nov 10, 2013)

beenthere said:


> They are suppose to run in first stage most of the time. Hard wear and tear on the compressor is from starting and stopping.
> 
> Read the below article on Snowball. It ran non stop for 28 years.
> 
> https://www.trane.com/residential/en/why-us/testing-facility.html


Thank you for this.


I took your advice and set it up for long running times. Took the bypass off of stage 1 and I also dropped CPH down to 1 (It was at 2).

It still cycles a bit at -10c but running times are much longer now and the house temperature is much more even. The defrost sessions now actually have time to complete before heat demand ends.

Overall it seems to be functioning much more evenly. Of course I still hate the idea of it running when it doesn't need to but clearly that's all in my mind.

Your way definitely works better.


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## beenthere (Oct 11, 2008)

Long long run times is why modulating furnaces make a home feel more comfortable. 

Modulating heat pumps do the same thing. Carrier has 5 steps of modulation. Virtually never shuts off, but still saves a large amount on the heating bill.


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## Bob Sanders (Nov 10, 2013)

The rheem system seems to be functioning much better with the long runs so I take back what I said... so probably more operator error than the rheem system. It does take things to the extreme a bit more than goodman's timed system. It allows for a pretty good layer of frost before a defrost session. There is about a degree drop in duct outlet temp before the rheem defrost kicks in I caught it just as it was going into defrost (sorry the images aren't the clearest... it's snowing right now):


























What concerns me though is the ice build up which is starting to occur in the bottom of the machine. The coil around the edges has lots of drainage holes but there is not really much in terms of drainage towards the center of the machine. The water never really makes it far enough inside the machine before it freezes anyway.
At what point should I be concerned about this and how are others handling it?


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## WyrTwister (Jul 22, 2013)

I would set the condenser on concrete blocks , instead of a wooden box .

Then , if you want the bottom of the condenser sheet metal to drain , drill a weep hole in it .

God bless
Wyr


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## Bob Sanders (Nov 10, 2013)

Well I think (weather providing) I'll just take the fan off and run some holes straight through the condenser tray AND the wood. I'm a little surprised though that goodman only supplied good drainage on the edges where the coil is and did not really consider the center of the machine. Other than mounting holes there really is no drainage and the tray is kind of sectioned off with ridges (added strength for the tray)


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## beenthere (Oct 11, 2008)

Usually don't have that much build up. But I out them on pump ups. So the bottom gets a little warming from the coil and melted ice. Being on a platform, the platform is too much mass for the water to warm up.


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## Bob Sanders (Nov 10, 2013)

beenthere said:


> Being on a platform, the platform is too much mass for the water to warm up.


I may be wrong but I think the opposite would be true... with wood anyway. It's not the best insulator in the world but it does shield from the cold.

Anyway, I think the big issue is just plain lack of drainage in the bottom of the tray. It should slowly clear up on its own once the temp goes down and stays down, but there is a fair bit of defrosting going on when our temp is bouncing up and down between 0c and -10c like it has been. Last night it only needed defrosting once from 11p to about 5am this morning (only one defrost noted on the counter this morning), but our temp is now -2.5c and defrosting is happening about every 3 hours or so (clock time).


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## beenthere (Oct 11, 2008)

Its not that the wood is insulating. Its that the wood is also at ambient temp. And taking enough heat out of the water for it to freeze again.


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## Bob Sanders (Nov 10, 2013)

Nope... I go back to what I said before. The rheem defrost board works great down to about -6C (21F), after that it starts becoming unreliable. The temp went down to about -11C (12F) last night and the counter showed it had defrosted 6 time (in about 8 hours). I caught the last of those defrost sessions early this morning and there wasn't a stick of frost on the coils. I don't know how rheem is figuring frost build up by comparing coil and air temperatures but it appears to be completely inaccurate at lower temperatures (in our climate anyway).

I have reconnected the goodman system and I'll live with that until next season, then I'll play around with demand defrost on a differential pressure basis. It seems in theory anyway, that that would be one of the most reliable ways to go.


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## beenthere (Oct 11, 2008)

The Rheem defrost board expects 400 CFM air flow per ton at the indoor unit.


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## Bob Sanders (Nov 10, 2013)

beenthere said:


> The Rheem defrost board expects 400 CFM air flow per ton at the indoor unit.


I'm not sure I follow that.
CFM does not change at -5 vs -10. It's the same. It's on low stage at both temps. 

It does a good reliable job to about -6 and then becomes unreliable...cfm has not changed


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## beenthere (Oct 11, 2008)

Bob Sanders said:


> I'm not sure I follow that.
> CFM does not change at -5 vs -10. It's the same. It's on low stage at both temps.
> 
> It does a good reliable job to about -6 and then becomes unreliable...cfm has not changed


It effects coil temp of the outdoor coil. 

It could also be caused by the position of the coil temp sensor.


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## Bob Sanders (Nov 10, 2013)

beenthere said:


> It effects coil temp of the outdoor coil.


Understood. But as stated cfm is not changing. If cfm was a factor then I don't see how the rheem board would not be adversely affected in all ranges.



> It could also be caused by the position of the coil temp sensor.


Coil sensor has been moved several times now.


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## beenthere (Oct 11, 2008)

Bob Sanders said:


> Understood. But as stated cfm is not changing. If cfm was a factor then I don't see how the rheem board would not be adversely affected in all ranges.
> 
> Coil sensor has been moved several times now.


Outdoor coil should be flooded more in colder weather. Lower indoor air flow may be preventing that.


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## Bob Sanders (Nov 10, 2013)

beenthere said:


> Outdoor coil should be flooded more in colder weather. Lower indoor air flow may be preventing that.


Well, I'm not sure I agree with that but I suppose I could experiment with it and run in high stage at full cfm and see if it makes a difference. Not sure it's worth it though... I'm thinking the best way to handle this under all conditions is simply to use differential pressure. If the coil is plugged with frost the pressure has to change. If it's not then the pressure doesn't change.


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## beenthere (Oct 11, 2008)

Whirlpool(when they made heat pumps, back in the 70s) used that method successfully.


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## Bob Sanders (Nov 10, 2013)

Okay, so I wasn't going to get into this until next season, but I got a couple of warm days coming up next week and I have all the parts so what the heck.... I figured I may as well through together a pressure differential system and play around a little next week.

I'm using the same concept I used with the rheem board... instead of replacing the existing heavily integrated stock defrost board, I'll simply fool the goodman board into thinking it doesn't need defrosting and then hand that job off to the new pressure differential board.










It's pretty simple...
1) is the differential pressure switch which will sense a vacuum within the casing as the coil plugs with frost

2&3) form the necessary 4 second pulse to the goodman board to trigger a manual test defrost.

4) is the connect for the 4 second pulse to the goodman board.

5) is where the goodman coil sensor will connect. Usually it connects directly to the goodman board, but during normal heating operation I have to make sure the goodman board does not go into defrost so relay 6 will alternate (at appropriate times) in and out a dummy 27K resistor which reports 40 degrees F to the goodman board (above freezing) so it can't go into defrost mode.

6) This relay is connected to the reversing valve. In its relaxed position it sends an 'above freezing' signal to the goodman so it does not go into defrost.
When a defrost is triggered, the rv is of course enrgized which will pull this relay in at which point reconnects the coil sensor directly to the goodman board and it will now get an accurate reading on the coil. When the coil hits the required 70F to end the defrost cycle the rv and relay 6 will be deenergized reconnecting the dummy resistor.

7) is simply a connection for a digital counter I have at the air handler to keep track of the number of defrosts.

It's been bench tested and works so I don't see any issues on the machine. I think the only trick will be setting up the pressure switch. I haven't done any differential pressure measurements at all on the condenser so I don't know how much of a vacuum it will create, but it SHOULD create enough to trigger the switch if set properly... although I may have to spend a bit of time making the casing a bit more air tight.

My other concern is the diaphragm inside the pressure switch. The specs say it's good down to -40F but I can't help but think the cold might change the switch's sensitivity as the diaphragm stiffens as it cools.... we'll find out though I guess.


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## Bob Sanders (Nov 10, 2013)

Installed the new pressure controlled defrost system today, and it seems to work. Won't know for sure until it gets frosty again. It's +5C today... amazingly enough, so I had to simulate a build up of frost by wrapping a big piece of cardboard around the machine. Got about half way around the condenser with the cardboard when it kicked into defrost mode so it looks pretty good. It might need some fine adjustment when the frost comes but that should be about it.

Had a heck of a time setting up the differential pressure switch though. Apparently (and I didn't know this) but there is a fairly wide variation of pressure differences within the casing so finding the right location for the the pressure sensor tube was a real headache. Finally found the ideal location to be up into the fan shroud (Blue Tubing)


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## WyrTwister (Jul 22, 2013)

So , you are controlling , according to differential in air pressure ? Comparing aor pressure outside the cabinet / housing to that at some point inside , where the compressor is ?

God bless
Wyr


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## Bob Sanders (Nov 10, 2013)

WyrTwister said:


> So , you are controlling , according to differential in air pressure ? Comparing aor pressure outside the cabinet / housing to that at some point inside , where the compressor is ?
> 
> God bless
> Wyr


Correct.
One side of the differential pressure switch is open to atmosphere (outside the casing) and the other side is inside the casing (where the compressor is). As the coil plugs with frost the condenser fan causes the pressure to drop inside the casing as compared to outside the casing. When the pressure drops enough a defrost is triggered.


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## zappa (Nov 25, 2011)

I like it...does the Goodman board force a defrost after so many hours?


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## Bob Sanders (Nov 10, 2013)

zappa said:


> I like it...does the Goodman board force a defrost after so many hours?


I have no idea. I'm assuming you're thinking about oil return?

I looked for an answer a while back and couldn't find anything. Neither the operating manual or the maintenance manual says anything about a forced defrost. It's strictly timed defrost BELOW 31 degrees. If at any time the coil comes above 31 degrees the timer resets/stops

I will say that in all the time I had it operating above 31 degrees I have never seen it go into defrost... so I'm thinking NO.


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## beenthere (Oct 11, 2008)

The Goodman is a time and temp board. It has no forced defrost every 6 hours, since it defrost every X minutes whether needed or not.


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## Bob Sanders (Nov 10, 2013)

beenthere said:


> It has no forced defrost every 6 hours, since it defrost every X minutes whether needed or not.


No it does not.
It is timed defrost when the coil goes *BELOW* 31 degrees. There is no defrost that I can see above 31.

The manual states that every few minutes the sensor checks the coil temperature to see if it is below 31 degrees. If it is below 31 it starts the timer. If at any time the coil goes above 31 it resets the timer.

So if ambient is above 31 and the condenser stops long enough for the coil to go above 31, the timer resets. It is entirely possible to go with no defrost at all so long as the coil goes above 31 degrees at some point before the timer runs out.


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## beenthere (Oct 11, 2008)

Bob Sanders said:


> No it does not.
> It is timed defrost when the coil goes *BELOW* 31 degrees. There is no defrost that I can see above 31.
> 
> The manual states that the sensor checks the coil temperature to see if it is below 31 degrees. If it is below 31 it starts the timer. If at any time the coil goes above 31 it resets the timer.


Which in the trade is considered defrosting whether it needs it or not. Since the coil temp can drop below 31°F even when it is 40°F outside. And defrost by the warm air temp. But the defrost board goes into defrost anyway. If the compressor's accumulated run time equals what the board is set for(happens a lot on the ones that the people use temp set back).

All time and temp defrost boards have a cut off temp that above it, it doesn't defrost.


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## Bob Sanders (Nov 10, 2013)

beenthere said:


> And defrost by the warm air temp. But the defrost board goes into defrost anyway. .


No it doesn't.
The timer does not lock in. If at any time the coil goes above 31 the timer resets.
If it's 40 degrees out and the coil will go below 31 at which point the timer starts. But if the machine stops and the coil warms up, the timer is reset again.


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## beenthere (Oct 11, 2008)

Bob Sanders said:


> No it doesn't.
> The timer does not lock in. If at any time the coil goes above 31 the timer resets.
> If it's 40 degrees out and the coil will go below 31 at which point the timer starts. But if the machine stops and the coil warms up, the timer is reset again.



Thats why I said about it happens on one that people use temp set back. Because when the stat goes into recovery. They will run long enough to go into defrost.


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## Bob Sanders (Nov 10, 2013)

beenthere said:


> Thats why I said about it happens on one that people use temp set back. Because when the stat goes into recovery. They will run long enough to go into defrost.


Yes.
If it runs long enough so that the coil is still below 31 when the timer times out then it will most definitely go into defrost mode.


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## zappa (Nov 25, 2011)

So by adding the pressure switch, and during the right weather conditions, I'm thinking it could run for a very long time with no defrost?


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## Bob Sanders (Nov 10, 2013)

zappa said:


> So by adding the pressure switch, and during the right weather conditions, I'm thinking it could run for a very long time with no forced defrost?


If all conditions are right then it is possible it will not go into defrost mode for a long period of time. But the same is true under the goodman system if it operates slightly above 31 and the machine doesn't run for long periods.


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## zappa (Nov 25, 2011)

It's different though. If the timer resets that means it's warmer and the oil can flow. If you have a long period of cold dry weather there will be no 6 hour forced defrost.

I can't say how important it is other than what I've read but the designers must feel it's important.


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## Bob Sanders (Nov 10, 2013)

zappa said:


> It's different though. If the timer resets that means it's warmer and the oil can flow. If you have a long period of cold dry weather there will be no 6 hour forced defrost.
> 
> I can't say how important it is other than what I've read but the designers must feel it's important.


Well... refrigeration oil can flow at stupidly low temperatures, but oil return is a valid concern, and if it looks like it's going to be days until it goes into defrost mode at lower temperatures, then I may have to add a one shot resettable timer and force a defrost every 8 or 10 hours or so.


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## beenthere (Oct 11, 2008)

The refrigerant flow concern isn't caused by low outdoor temp per say. Its due to the lower velocity through the coil at colder temps. Thats when the oil can separate from the refrigerant and just stay in the coil.


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## Bob Sanders (Nov 10, 2013)

beenthere said:


> The refrigerant flow concern isn't caused by low outdoor temp per say. Its due to the lower velocity through the coil at colder temps. Thats when the oil can separate from the refrigerant and just stay in the coil.


True.
But at some point when there is enough oil in the coil it will get slugged along whether it likes it or not. Now that's not to say that a forced defrost can be avoided. You do NEED to warm up that coil every so often to avoid oil slugging because it causes a certain amount of inefficiency.


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## Bob Sanders (Nov 10, 2013)

It went down below 31 last night about 8pm and now (13 hours later) the counter shows 2 defrosts, so the system does seem to be working. The Goodman system would have produced at least 4 defrosts, and the rheem system proved completely unreliable in my circumstance so this looks good.

Just in case it starts looking like long periods of time between defrosts, I ordered a timer and will incorporate that so that if a defrost does not occur in say... about 10 hours or so, then a forced one will occur.


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## beenthere (Oct 11, 2008)

All on demand defrost boards force a defrost at 6 hours if none occurred when its cold outside. While I am sure they left some room in for safety. I don't think they left a 166% safety margin.


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## Bob Sanders (Nov 10, 2013)

6 hours (IMO) is too often... so I'll split the difference with ya and say 8


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## Bob Sanders (Nov 10, 2013)

So it's been about a week. I haven't been able to test in the real cold yet. We have been hovering around 34 to 28 F (unheard of this tie of year) but so far, so good. This system (with the timer coming)looks like the real deal, but I have run into a real interesting 'plateau' I thought I would mention....

As the coil starts plugging a vacuum starts forming inside the casing which the pressure sensor picks up on. But if I let the coil get TOO plugged the vacuum actually hits a plateau and then starts getting weaker. I do not have an ecm motor on my condenser. It's a PSC so at a certain point in time instead of vacuum continuing to increase , it hits a plateau and then begins to drop because the motor begins to slow with the higher wind resistance. An ecm motor would pick up on this and increase the amperage, but not a psc... it's too dumb for that. At this point in time the condenser is now free to turn into a block of ice.

If I had an ecm motor then setting up the pressure sensor would be a piece of pie but because I don't I have to be really careful not to overshoot the adjustment on the pressure sensor.

Pretty bloody interesting. I had no idea that was going to happen!


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## user_12345a (Nov 23, 2014)

If you let your coil get too dirty it won't defrost at the right time any more.

Do the condenser ecm motors really ramp up and down to maintain airflow? not sure if they're programmed to do that. 

ecm in the condenser is a huge overkill and bad idea all around. think of the repair costs.


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## beenthere (Oct 11, 2008)

As the coil frost up. The fan recircs air inside the unit(sometimes you can feel it blowing out the side of the unit near the top). Centrifugal force throws more air off the side of the blades then when the coil is frost free. Its the lower volume of air that causes it to happen. Its very noticeable in the summer in cooling mode with real dirty coils. Very little air is thrown up as you get closer to the center of the fan blades.

Where are the hoses for your pressure switch located at.


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## Bob Sanders (Nov 10, 2013)

There are pictures in post 146.

Just to the right of the fan underneath the top of the machine. That blue tube curving upwards. It ends about a half inch from the underside of the top of the unit. It SHOULD be the lowest pressure there.


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## Done That (Apr 28, 2011)

The factory control board can be wired to and control a 2-speed ECM condenser fan motor, Goodman uses them on some units for efficiency. But as User_12345a states, they are not usually programmed to ramp in the same way as an ECM indoor blower does.


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## Bob Sanders (Nov 10, 2013)

Done That said:


> The factory control board can be wired to and control a 2-speed ECM condenser fan motor, Goodman uses them on some units for efficiency. But as User_12345a states, they are not usually programmed to ramp in the same way as an ECM indoor blower does.


It is a 2 speed. It ramps up when it goes to 2nd stage.


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## Done That (Apr 28, 2011)

Yes, you have a 2-speed PSC OD fan that changes with the compressor stage.

I'm just saying 2-speed ECM OD fan was also made at the factory. But again, I do not believe they are set up provide constant CFM (which is what I meant by "ramp").

Simply responding to your comment that it would be a piece of pie if it had ECM.


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## beenthere (Oct 11, 2008)

Whirlpool use to use a pressure switch for defrost control. Just can't remember if they used a low negative pressure, or high negative pressure.

The more I think about it. I think it was when the pressure difference decreased, it went into defrost.


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