# HVAC system heat won't run with standby generator running...



## PTighe (Jun 4, 2009)

I had my licensed electrician install a Generac Guardian 18 KW air cooled standby outside generator powered by LPG and it works great.

Then I had an HVAC contractor install a Lennox signature series furnace and AC with all the bells and whistles, including motorized dampers for 2 zone heating/AC which are run by an internal computer inside the furnace.

The problem is...when the power goes out, the generator kicks on in 15 seconds and lights the house back up, but the heat won't work! The AC works fine but an error code keeps coming up on the furnace when the heat tries to kick in.

Both of my contractor's have been trying to fix this problem for six months and still it won't work. Both of them say the computer in the furnace doesn't like the "dirty" power coming out of the generator.

It's at the point now where they have given up and the HVAC contractor is taking entire responsibility for the whole works, including replacing everything at his cost for a generator/furnace system that WILL work when the generator. Does anyone know of a combination of furnace and generator (air cooled) which work together with no problems? The Lennox and Generac factories haven't been able to come up with a solution either. Thanks, PT


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## vsheetz (Sep 28, 2008)

I assume you have tried running the HVAC through a battery backup with power conditioning?


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## J. V. (Jun 1, 2007)

It looks like all those bells and whistles have come back to bite you. The AC computer evidently does not like the quality of power your generator is making.


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## Yoyizit (Jul 11, 2008)

PTighe said:


> I had my licensed electrician install a Generac Guardian 18 KW air cooled standby outside generator powered by LPG and it works great.
> 
> The AC works fine but an error code keeps coming up on the furnace when the heat tries to kick in.
> 
> ...


You should probably put a scope on the gen. power when the heat tries to start, although this 75A gen. should be able to handle it.
It's a lot easier to filter the power going into the HVAC computer (provided this error code is a "false positive") than it is to changeout the whole setup.

Too bad you don't live closer to DC.


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## jogr (Jul 24, 2007)

It's great that the HVAC guy is going to take care of you. I bet most of the time there would be a lot of finger pointing between the generator guy and the HVAC guy and no one taking responsibility. It's good to hear about standup contractors. I wish I could help but electronics is definitely not my forte. Since one of the major reasons for backup power is to maintain house conditioning I'm surprised that Lennox and Generac don't already have this figured out.


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## jogr (Jul 24, 2007)

After reading Yoyizits and vsheetz posts I wonder if they can isolate the computer power from the rest of the furnace and put a computer type battery backup on it??


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## jerryh3 (Dec 10, 2007)

vsheetz said:


> I assume you have tried running the HVAC through a battery backup with power conditioning?


I was thinking that also. It would be a cheap fix if it worked. Is there 240V or 120V running to the furnace? I'm sure the controls work off of some transformer that doesn't like the gen power.


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## Yoyizit (Jul 11, 2008)

Once the heat is going it might tolerate generator power but I don't know of an easy way to test this theory. The xfer process itself may set off an error code.

You need the particulars of how your error code is set. The ball is in Lennox's court to provide this (proprietary?) info.

Or, you may just need a single point ground, in the sense that heavy startup current is changing the voltage on the signal ground of the HVAC computer and the computer is interpreting this change as a valid signal. 
This not something most people would look for because the schematic is being and has been followed. The fix may be as simple as moving a wire from one terminal to another.
You definitely need a scope for this one. And, I would have expected this on A/C startup, instead.


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## MALCO.New.York (May 29, 2009)

Certainly need a Conditioner before you go and FRY that PC Module!!


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## PTighe (Jun 4, 2009)

Thanks for your comments; there are a few items that I forgot to mention. When the heat didn't come on when the generator kicked in, the contractor bought an ACME line conditioner and hooked it up which conditioned the entire furnace but it didn't solve the problem. The tech also checked out the sine wave with an oscilloscope and it was basically uniform. The electrician added multiple grounds as requested by the HVAC contractor, which did nothing. 

Then he borrowed an UPS unit to see if it would work and it didn't. Then he bought a Liebert "true" UPS unit for computers, hooked it up and it didn't work either. The tech was so disgusted he left it here next to the furnace while they work on plan C.

I don't think there is any fix for this problem excepting yanking the new furnace and replacing it with a "low tech" unit without all the computer bells and whistles and then it will work. There must be a Lennox or comprable model that will run correctly when running off the generator. I have Alleghany Power, which is just as "dirty" as the power from the generator. What do you think...go ahead and replace the furnace or keep trying out new "theories". They have been trouble shooting this since January to no avail. I want them to fix this now before it drags out too long. Thanks, PT


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## jerryh3 (Dec 10, 2007)

Is the furnace running when they are doing the switch-over tests? I wonder if the furnace has a lockout that is preventing it from restarting so soon once it loses power? This is a LP furnace, right? You may want to try to ask over at the www.hvac-talk.com forum to see if anyone over there has heard of this.


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## PTighe (Jun 4, 2009)

jogr said:


> I'm surprised that Lennox and Generac don't already have this figured out.


The electrician who installed the generator is an authorized Generac installer and went to their school and is certified to install these generators. He has called them several times and they don't have a clue; the HVAC guys did the same with Lennox, nothing. PT


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## Billy_Bob (Sep 11, 2008)

You need an "online" true sine wave UPS. This makes electricity ALL the time whereas other UPS only make electricity when power is removed.

FYI here is what dirty power looks like...
http://www.jkovach.net/projects/powerquality/


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## PTighe (Jun 4, 2009)

jerryh3 said:


> Is the furnace running when they are doing the switch-over tests? I wonder if the furnace has a lockout that is preventing it from restarting so soon once it loses power? This is a LP furnace, right? You may want to try to ask over at the www.hvac-talk.com forum to see if anyone over there has heard of this.


These guys have tried it every which way there is; it is an LP furnace with a 500 gallon underground tank supply to the house and dedicated only for the furnace. Once you switch the furnace off it off, it takes about 10 minutes for all this computer coding to "recycle", then it comes back on. They got a reading of about 13" of head on their manometer at the furnace, so it has plenty of gas going into the furnace. I give up.


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## jerryh3 (Dec 10, 2007)

PTighe said:


> These guys have tried it every which way there is; it is an LP furnace with a 500 gallon underground tank supply to the house and dedicated only for the furnace. Once you switch the furnace off it off, it takes about 10 minutes for all this computer coding to "recycle", then it comes back on. They got a reading of about 13" of head on their manometer at the furnace, so it has plenty of gas going into the furnace. I give up.


Yep. Sounds like they tried everything. Again, try the HVAC forum. They may have a suggestion or two.


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## Yoyizit (Jul 11, 2008)

Try switching out the Lennox control board that gives you the error code. It may be hypersensitive.

Otherwise you need the board schematic (you'll probably have to sign a non-disclosure agreement) and one of these
http://www.pctestinstruments.com/

These guys are stumped, but their troubleshooting method was by replacement. Since everything else was tried, I'd say it was a grounding problem. 
I'd do the minimum grounding required for it work and debug this config. if necessary, and then cautiously build back up to an NEC ground system.

I'd love to tackle this one. . .maybe twice in my life I faced a problem like this.


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## PTighe (Jun 4, 2009)

Billy_Bob said:


> You need an "online" true sine wave UPS. This makes electricity ALL the time whereas other UPS only make electricity when power is removed.
> 
> FYI here is what dirty power looks like...
> http://www.jkovach.net/projects/powerquality/


I _think_ that the Liebert UPS that is sitting my basement now is the same as what you mentioned above. The tech installing it got sine wave that looked like this also. PT


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## Yoyizit (Jul 11, 2008)

PTighe said:


> I _think_ that the Liebert UPS that is sitting my basement now is the same as what you mentioned above. The tech installing it got sine wave that looked like this also. PT


You may need a storage scope because almost certainly you are looking for a transient. That's what logic analyzers do; capture the transient that caused the problem. In your case you may need one that runs on batteries so it is totally isolated from the AC line.


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## ScottR (Oct 6, 2008)

"Dirty power" sounds like BS to me -- especially because they checked it with a scope and tried a Liebert double-conversion online UPS.

I don't know why they wouldn't try a new controller board before ripping out the entire system -- did they?

My only other thought is that there is something attached to the control computer (circ. pump, temp. sensor package, damper motor, etc) that is getting power from the mains panel and is not getting switched to generator along with everything else. That's unlikely, and even more unlikely that 2 contractors missed it, but possible.


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## PTighe (Jun 4, 2009)

ScottR said:


> "Dirty power" sounds like BS to me -- especially because they checked it with a scope and tried a Liebert double-conversion online UPS.
> 
> I don't know why they wouldn't try a new controller board before ripping out the entire system -- did they?
> 
> My only other thought is that there is something attached to the control computer (circ. pump, temp. sensor package, damper motor, etc) that is getting power from the mains panel and is not getting switched to generator along with everything else. That's unlikely, and even more unlikely that 2 contractors missed it, but possible.


Yes, they did put new computer controller board on the wall, the one with the flashing function lights, that didn't fix it either. You guys are starting to talk over my head on this! It would help if I was an EE.







I'm going to call them tomorrow and see what they're going to do, since they are picking up the tab. BTW, this HVAC company is very large with about 50 employees, not one guy and a helper.

I appreciate everyones comments but my original question was...did anyone here know of a combination of generator/HVAC system that they KNOW works during a power outage? PT


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## ScottR (Oct 6, 2008)

PTighe said:


> .did anyone here know of a combination of generator/HVAC system that they KNOW works during a power outage?


This model has an almost 100% chance of starting up during a power outage...










:laughing:


Seriously though, if Lennox and Generac guys are telling you that your current setup _should_ work, I dunno...


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## micromind (Mar 9, 2008)

I've installed a bunch of generators, though the smallest is around 50 KVA. 

In my experience, most fancy electronic things (including UPSs) are very picky about their power supply. They want the voltage to be maintained within about 10% or so, even when starting a compressor. Very few generators can start a motor of any size without a considerable voltage dip. 

They also want the frequency to be very close to 60 HZ. A lot of them will fail if the frequency gets below 59.5 HZ, or above 60.5. Unless there's an electronic governor on the gen, the frequency is likely somewhere between 55-65. 

The older mechanical HVAC units had no problems with these power fluctuations, but the newer electronic ones won't tolerate it.

Rob


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## Yoyizit (Jul 11, 2008)

micromind said:


> In my experience, most fancy electronic things (including UPSs) are very picky about their power supply.
> They want the voltage to be maintained within about 10% or so, even when starting a compressor. Very few generators can start a motor of any size without a considerable voltage dip.
> 
> They also want the frequency to be very close to 60 HZ. A lot of them will fail if the frequency gets below 59.5 HZ, or above 60.5. Unless there's an electronic governor on the gen, the frequency is likely somewhere between 55-65.
> ...


OK, so the AND function which is giving the Power Bad signal has at least two inputs: RMS voltage and freq. I suppose with a generator you could have problems with both, on startup.
Maybe there is a factory setting for the control board that loosens the spec's for power quality.
To fix the generator's capability to handle transient loads probably would at least require a large flywheel.


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## InPhase277 (Feb 9, 2008)

It may indeed be a frequency related problem. Maybe the fix is something like powering the control board with a small true sine inverter.


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## ScottR (Oct 6, 2008)

I'm still not buying the dirty power reasoning.



> Then he bought a Liebert "true" UPS unit for computers, hooked it up and it didn't work either.


I gotta assume from that description that it was a double conversion, online, true sine wave UPS. There's no way that crap generator power would get past it. If the input power fell out of the UPS's spec range it would switch over to batteries. If it stayed on batteries for too long, it would shut down. The controller module would only see near-flawless power, or no power.


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## biggles (Jan 1, 2008)

make sure you have a solid ground wire from the generator to the furnace


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## Billy_Bob (Sep 11, 2008)

Actually not having "pure power" is a problem in the automotive area as well! They have had problems with A/C spikes wrecking the vehicle "programming" process.

When "programming" vehicles with new software, the process can take quite awhile and drain car batteries, so an external source of power is needed for the vehicle. But they are quite picky about the external power source being used to "jump" the car battery during programming...

http://www.ereleases.com/pr/midtronics-supply-essential-programming-tool-gm-hybrids-13474


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## Yoyizit (Jul 11, 2008)

"Progress" is a myth. :laughing:


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## Zoandar (Jun 27, 2009)

This is all very interesting, because I am having the same issue, that my A/C won't start when on my generator. With my case, the A/C and generator DID work together just fine before we got a new furnace installed. Now with the new furnace the A/C clatters the furnace control board relay and then trips its breaker, all while pulling the full-time blower down to a crawl speed.Having read this thread, the only solution seems to be to make a totally separate control circuit for running my A/C only when on the generator, completely outside any connection with the furnace controlller.Oddly, the furnace runs just fine on the generator. Just the opposite of this fellow's problem.


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## Yoyizit (Jul 11, 2008)

Zoandar said:


> the A/C clatters the furnace control board relay and then trips its breaker, all while pulling the full-time blower down to a crawl speed.


This brings up another thought. 

The control circuitry of the HVAC and the generator are probably quite sophisticated, which may result in each system trying to accommodate to the other, possibly resulting in "hunting." This you might see on a scope, briefly.

Each system works by itself in factory tests, but when hooked together they become underdamped. If the resulting oscillation grows without limit one or the other unit would shut down or be damaged. Substantially increasing the elec. load on the generator should change this pattern.
Generally you want "critical damping," where any oscillation quickly dies out.

The clattering system hung on for a while but the other one bailed out at the first sign of trouble.

With more and more HO generator systems this problem may start showing up in more places.


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## Zoandar (Jun 27, 2009)

Looks like a good place for one of those old round Honeywell thermostats and a separate 24 V supply, taking the furnace's A/C controller out of the picture.


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## wirenut1110 (Apr 26, 2008)

I realize this post is a little old but here goes anyway. 

If you have the model 5416 18 KW generator, and you think it's a frequency issue, you can adjust this by the potentiometer on your voltage regulator board. Refer to your owners manual section 2.7 and it will explain how to do this. Voltage and frequency are directly proportional (2-1 ratio) so if your generator output voltage is 124 volts then the frequency is 62 Hz. 

If you don't feel comfortable doing this go to http://generac.com and locate an authorized dealer in your area.

If you don't have an owner's manual, here's one for you Model 5416 18 KW give it time to load, it takes a while on my computer.

An added note, your generator does have an electronic governor.


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## Yoyizit (Jul 11, 2008)

The manual posted above does give a clue to how tight the freq. is controlled. If no load gives 62 Hz you could infer that full load gives 58 Hz. If your furnace is looking for 60 Hz within a tighter tolerance than +/- 1 or 2 Hz, either on a steady-state basis or a transient basis, it won't get along with this generator.

I think the transient response (step response) of the generator is important in this application, and it's not given.
I'm looking for a generator spec'n like 
http://www.expertune.com/images/ArtCharactFig4.gif
or
http://en.wikipedia.org/wiki/File:High_accuracy_settling_time_measurements_figure_1.png
except the horizontal scale would be time in milliseconds or tenths of a second and the vertical scale would be freq. or voltage, and the graph would show temporary deviations from the steady-state values.

The generator people might be able to advise you on what loads are likely to cause generator instability.


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## PTighe (Jun 4, 2009)

wire nut 1110 said:


> I realize this post is a little old but here goes anyway.
> 
> If you have the model 5416 18 KW generator, and you think it's a frequency issue, you can adjust this by the potentiometer on your voltage regulator board. Refer to your owners manual section 2.7 and it will explain how to do this. Voltage and frequency are directly proportional (2-1 ratio) so if your generator output voltage is 124 volts then the frequency is 62 Hz.
> 
> ...


Thanks wire nut 1110 but I'm not an electrician. This Wednesday July 1st, the HVAC Service Manager and his lead Tech will meet out here with a different Electrician _*they hired*_ for a second opinion. He also is an authorized Generac dealer who is certified to work on these units. He will test everything on the generator while on the phone with the Generac Factory Tech advisor.

If something doesn't pass with the testing, Generac will send a Factory tech to my place with the guys above and check out himself. I have no say in this at all as the Dealer is handling everything now at his expense. All I can say at this point is that this exercise is getting pretty old. (Since January).

I have also heard though from the Dealer that on May 27th, Lennox issued a service bulletin to all of their dealers...that from now on, Lennox will not guarantee any of their products to work when used in conjunction with any standby generator. This doesn't make any sense though since Lennox has their own brand of generators that have the Lennox name on it but are actually manufactured by Generac. Go figure. PT


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## Yoyizit (Jul 11, 2008)

PTighe said:


> Thanks wire nut 1110 but I'm not an electrician. This Wednesday July 1st, the HVAC Service Manager and his lead Tech will meet out here with a different Electrician _*they hired*_ for a second opinion. He also is an authorized Generac dealer who is certified to work on these units. He will test everything on the generator while on the phone with the Generac Factory Tech advisor.
> 
> If something doesn't pass with the testing, Generac will send a Factory tech to my place with the guys above and check out himself. I have no say in this at all as the Dealer is handling everything now at his expense. All I can say at this point is that this exercise is getting pretty old. (Since January).
> 
> I have also heard though from the Dealer that on May 27th, Lennox issued a service bulletin to all of their dealers...that from now on, *Lennox will not guarantee any of their products to work when used in conjunction with any standby generator.* This doesn't make any sense though since Lennox has their own brand of generators that have the Lennox name on it but are actually manufactured by Generac. Go figure. PT


That's the problem; each unit by itself meets factory specs. It's when they play together the problem shows up.
If the clues point to costly redesigns of HVAC & Gen control circuitry the people pursuing the problem will suddenly be struck blind, deaf and mute. It's called "aggressive disinterest."


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## Zoandar (Jun 27, 2009)

I am not an electrician either, but I'll bet the entire issue lies in the design of the controller board depending upon what some caprice engineer ass-umed to be a "constant" in regard to line voltage and frequency, and it uses those values to compute some essential function, instead of adding in the circuitry it would need to calculate those values on its own. (To save a few pennies, no doubt.) The generator power "changes" the constants, so the system can't work. 

I agree with the aggressive disinterest theory. And I find it particularly interesting to read of Lennox's tech bulletin release. Clearly they are setting up a loop-hole for any future issues of a similar nature instead of simply FIXING their flawed design so it can work with "imperfect" generator power.

So when was Generac's service bulletin released so as not to guarantee their generators will work with HVAC?


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## Yoyizit (Jul 11, 2008)

I think this interaction problem will come up more and more as everything gets more complex.

Some GFCIs don't get along with some motor loads, some AFCIs don't get along if there is a radio station nearby, etc. . . .

And don't forget the recent example we all have had about drug interactions.


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## PTighe (Jun 4, 2009)

Zoandar said:


> I am not an electrician either, but I'll bet the entire issue lies in the design of the controller board depending upon what some caprice engineer ass-umed to be a "constant" in regard to line voltage and frequency, and it uses those values to compute some essential function, instead of adding in the circuitry it would need to calculate those values on its own. (To save a few pennies, no doubt.) The generator power "changes" the constants, so the system can't work.
> 
> I agree with the aggressive disinterest theory. And I find it particularly interesting to read of Lennox's tech bulletin release. Clearly they are setting up a loop-hole for any future issues of a similar nature instead of simply FIXING their flawed design so it can work with "imperfect" generator power.
> 
> So when was Generac's service bulletin released so as not to guarantee their generators will work with HVAC?


I agree but I don't think it would cost "pennies" for Lennox to redesign their product, more like $$millions. This probably won't happen unless there is a class action lawsuit, so I'm not holding my breath.

To my knowledge, Generac has never issued any service bulletins, it was Lennox only. The service manager from the HVAC company said he would bring me a copy of the _*Lennox tech bulletin*_ when he comes out here on Tuesday.


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## wirenut1110 (Apr 26, 2008)

I checked Generac's dealer website this morning and saw no service bulletins, and I doubt there will be any.


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## PTighe (Jun 4, 2009)

Yoyizit said:


> I think this interaction problem will come up more and more as everything gets more complex.
> 
> Some GFCIs don't get along with some motor loads, some AFCIs don't get along if there is a radio station nearby, etc. . . .
> 
> And don't forget the recent example we all have had about drug interactions.


Exactly, I wish I still had my old LOW tech Lennox system back if I had known this fiasco was going to happen. The bottom line is the Generac works flawlessly in a power outage. All the lights come back on in the house; the hot water heater and the well pump work, along with the freezer and refrigerator, the garage door openers....everything except the furnace.


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## Yoyizit (Jul 11, 2008)

PTighe said:


> Exactly, I wish I still had my old LOW tech Lennox system back if I had known this fiasco was going to happen. The bottom line is the Generac works flawlessly in a power outage. All the lights come back on in the house; the hot water heater and the well pump work, along with the freezer and refrigerator, the garage door openers....everything except the furnace.


This is why I try to get appliances with electromechanical timers and no electronics.
Maybe vacuum tubes, which were inherently hardy, will make a comeback.:laughing:


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## PTighe (Jun 4, 2009)

Here is the Lennox Tech Service Bulletin they gave me shortly after I found out there was a problem back in January FWIW...


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## wirenut1110 (Apr 26, 2008)

It looks more like a ground issue than a frequency issue. Can you post a picture of inside the transfer switch.

I'm assuming you bought the pre-packaged 18 kw that came with a 200 amp SE rated switch.

P.S. I have a feeling something wasn't done when this switch was installed and a picture would confirm or deny this.


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## PTighe (Jun 4, 2009)

wirenut1110 said:


> It looks more like a ground issue than a frequency issue. Can you post a picture of inside the transfer switch.
> 
> I'm assuming you bought the pre-packaged 18 kw that came with a 200 amp SE rated switch.
> 
> P.S. I have a feeling something wasn't done when this switch was installed and a picture would confirm or deny this.


This system has about 3 separate grounds installed by my electrician in accordance with the bulletin above. Yes, they took it right out of the box. Pics below, this is the best I can do. PT


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## wirenut1110 (Apr 26, 2008)

Okay thanks, it wasn't what I was thinking because I thought you may have had the service rated transfer switch that came pre-packaged with that model.


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## wirenut1110 (Apr 26, 2008)

One more question, what was the output voltage on the generator load and no load?


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## Yoyizit (Jul 11, 2008)

You know, all grounds are not the same. 
A round conductor will have more impedance than a strap or braid or ribbon-shaped conductor.


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## PTighe (Jun 4, 2009)

wirenut1110 said:


> One more question, what was the output voltage on the generator load and no load?


I don't know, it was within the Lennox spec sheet above though. The electrician set the Generac to operate @ 60 Hz, within the operating range of the furnace...supposedly.


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## Yoyizit (Jul 11, 2008)

From that tech bulletin and my reading on flame rectification, the flame sensor must see between 1 and 10 uAdc from the 90 vac impressed across the flame.

Maybe there is so much ground noise that the control module can't see this tiny signal.


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## PTighe (Jun 4, 2009)

*Ok, everything is fixed today!!!!*

I haven't posted on this in a while because the electrician's and the HVAC guys have been trying trouble shoot this fiasco. The guy who originally installed this Generac Guardian 18kW generator gave up and said it was a problem with my Dave Lennox signature series furnace.

On the other hand, the HVAC guys said it was a problem with the generator because the Generac could not hold a steady, even 60 Hz when it was running. Long story short...the HVAC company hired their own Generac certified electician for a second opinion.

He came out here today along with the tech and service manager from where I bought the Lennox system. All them were out here for half a day trying different ways of correcting the problem...(the heat won't come on with the generator running).

The electrician called the Generac Tech line several times and finally they told him to *"turn on the #4 DIP switch" *which is in the generator unit. Well, guess what? It WORKS!!! The heat and the air conditioner both work fine now when running off the generator only.

It's taken seven months of trouble shooting and dozens of visits out here by these guys and the simple answer to such a complex problem was...turn on the #4 DIP switch, that really made my year. Anyone know what a DIP switch is? :thumbsup: PT


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## Yoyizit (Jul 11, 2008)

PTighe said:


> Anyone know what a DIP switch is? :thumbsup: PT


http://en.wikipedia.org/wiki/DIP_switch

The fourth switch evidently gooses some input to a microprocessor or logic array.

There has got to be a manual somewhere that explains what each switch setting does.


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## wirenut1110 (Apr 26, 2008)

Switch 1- On= low speed exercise Off= normal exercise
Switch 2- On=50 Hz Off=60 Hz
Switch 3-spare
Switch 4- On= 60 Hz operation Off= 58-62 Hz operation.


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## PTighe (Jun 4, 2009)

Yoyizit said:


> http://en.wikipedia.org/wiki/DIP_switch
> 
> The fourth switch evidently gooses some input to a microprocessor or logic array.
> 
> There has got to be a manual somewhere that explains what each switch setting does.


If a manual exists, these guys up here don't have it. I think Generac and Lennox are only interested in selling their products, not fixing or trouble shooting problems. That's why it took seven months to fix this problem, trial and error. That is just plain crazy. Fortunately for me, the HVAC company picked up the entire tab for this exercise. PT


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## PTighe (Jun 4, 2009)

wirenut1110 said:


> Switch 1- On= low speed exercise Off= normal exercise
> Switch 2- On=50 Hz Off=60 Hz
> Switch 3-spare
> Switch 4- On= 60 Hz operation Off= 58-62 Hz operation.


Thanks for the invaluable information. Duhhh, I'll have to send this to the two Generac electricians. :laughing:


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## wirenut1110 (Apr 26, 2008)

If they are dealers and have up to date diagnostic and repair manuals, this info is located on page 78 of the air-cooled manual. Just a little note, this feature and switch #2 is/was only available on the 18 KW.


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## Yoyizit (Jul 11, 2008)

This kind of incompetence comes along only once in a century. :thumbsup:


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## PTighe (Jun 4, 2009)

wirenut 1110 said:


> If they are dealers and have up to date diagnostic and repair manuals, this info is located on page 78 of the air-cooled manual. Just a little note, this feature and switch #2 is/was only available on the 18 KW.


Yes, they are both licensed Generac Dealers....Unbelievable :whistling2:


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## wirenut1110 (Apr 26, 2008)

Just an FYI, here's a pic in the manual.


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## Billy_Bob (Sep 11, 2008)

Edit: nevermind, I missed page two of the post...

What is the model number of the generator?

Trying to look at the owner's manual here...
http://www.generac.com/Service/ManualSearch/


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## PTighe (Jun 4, 2009)

wirenut1110 said:


> Just an FYI, here's a pic in the manual.


I've looked long and hard for the manual you reference above. Would you recall exactly which manual you got this from? Thanks in advance. PT


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## wirenut1110 (Apr 26, 2008)

Oh, I'm sorry. It's in a diagnostic and repair manual only available to dealers. I was referencing that for you to be able to show your dealer where it was.:thumbsup:


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## Wildie (Jul 23, 2008)

All electronics require direct current to operate! The furnace electronics will have a built in rectifier and filter to supply this!
I doubt that 'dirty power' is the root of the problem. The 'computer' power supply should be able to handle this!

I have experienced problems with generators that occurred during the initial starting period. The generators were able to support the running load, but failed to supply the starting current.
I would suggest that everything in the house be turned off and that the only load for the generator would be the furnace.
If the furnace still fails, it may be because of insufficient supply wire gauge. 
If the furnace is OK with all the other loads removed, perhaps the loads can be cascaded onto the generator with timers.


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## user62257 (Sep 12, 2009)

have any of you guys out there ever thought that it may be a frequency
issue.

As far as the dirty power, your brand is right up there.


A better brand of generator might work with your HAVC.


Like someone said, try the HAVC site.


The only thing in my bag of tricks, would some kind of relay set up,
that disconnects the HAVC for all power, and re-connects when the
generator is fully up and running. That may solve the freq. problem,
but not the dirty power problem. 

Good luck.

And please post back when you get this problem solved, will all would
like to know the anwer.


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## PTighe (Jun 4, 2009)

The problem was finally solved. The #4 DIP switch had to be turned on. Look at post #50 in this thread, back a page or two. Thanks to everyone for all their help. PT


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## kbsparky (Sep 11, 2008)

Ummm ... the problem was solved over a month ago! Post #50 stated thus:


PTighe said:


> I haven't posted on this in a while because the electrician's and the HVAC guys have been trying trouble shoot this fiasco. The guy who originally installed this Generac Guardian 18kW generator gave up and said it was a problem with my Dave Lennox signature series furnace.
> 
> On the other hand, the HVAC guys said it was a problem with the generator because the Generac could not hold a steady, even 60 Hz when it was running. Long story short...the HVAC company hired their own Generac certified electician for a second opinion.
> 
> ...


Scroll back on those threads before posting redundant information!

Edit to add: Looks like PTighe beat me to the punch!


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## Scuba_Dave (Jan 16, 2009)

wirenut1110 said:


> Switch 1- On= low speed exercise Off= normal exercise
> Switch 2- On=50 Hz Off=60 Hz
> Switch 3-spare
> Switch 4- On= 60 Hz operation Off= 58-62 Hz operation





PTighe said:


> Thanks for the invaluable information. Duhhh, I'll have to send this to the two Generac electricians


Of course you will charge them for the troubleshooting assistance :laughing:


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## user62257 (Sep 12, 2009)

The generator installers where not true electrician. A true electrician
would had check out the frequency of the product, when running and
up to speed.


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## user62257 (Sep 12, 2009)

*"Anyone know what a DIP SWITCH is?*

PTighe

I am trying to set up a link, to answer your question.

www.wikipedia.org/wiki/DIP_switch

I check the link above, what you know this one works.

Your DIP switch question will answer at the site this take you too.


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## Scuba_Dave (Jan 16, 2009)

4x - You keep posting answers to questions that have already been resolved

The Dip switch question (if it really was one ) was asked & answered over 5 weeks ago

_4x42001 - Your last post Violates the User agreement and has been removed_


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## PTighe (Jun 4, 2009)

Scuba_Dave said:


> 4x - You keep posting answers to questions that have already been resolved
> 
> The Dip switch question (if it really was one ) was asked & answered over 5 weeks ago
> 
> _4x42001 - Your last post Violates the User agreement and has been removed_


Sorry about that. I never intended to violate the agreement. Please delete this entire thread if you want.


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## Scuba_Dave (Jan 16, 2009)

PTighe said:


> Sorry about that. I never intended to violate the agreement. Please delete this entire thread if you want.


It wasn't you PTighe; it was a post by 4x42001 which has been removed


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## dnyberg2 (Dec 17, 2017)

Some generators emit high frequency noise on their outputs. Try a noise filter. A conditioner might not catch the HF stuff and that can drive a furnace controller board nuts as sometimes the clock that runs the microcontroller is derived off the 60HZ line. Go to Electronic Goldmine and search for filter. The Schaffner FN2010-10-06 Power Line Filter for $5 is a steal!


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## Oso954 (Jun 23, 2012)

His problem was fixed over 8 years ago.


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## kslattum (Dec 22, 2017)

I just encountered a similar issue with my HVAC ECM fan motor not running on generator power but resolved the issue in a different way. The 2016 Maytag hvac ECM fan in the fan coil would not run when my 2008 Generac 17kw generator would kick in. It was determined that the voltage being supplied by the generator (250-253V) was too high and the Maytag circuit was protecting the motor by not allowing the motor to start (no fault codes). My Generac generator didn't have dip switches like the one mentioned earlier in this post to change tolerance on frequency. It did have a potentiometer adjustment for voltage. Once the voltage was adjusted to ~240V, the ECM motor kicked in and ran without a problem. Hope this simple fix helps someone.


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## Blue Marjan (Oct 20, 2017)

kslattum said:


> I just encountered a similar issue with my HVAC ECM fan motor not running on generator power but resolved the issue in a different way. The 2016 Maytag hvac ECM fan in the fan coil would not run when my 2008 Generac 17kw generator would kick in. It was determined that the voltage being supplied by the generator (250-253V) was too high and the Maytag circuit was protecting the motor by not allowing the motor to start (no fault codes). My Generac generator didn't have dip switches like the one mentioned earlier in this post to change tolerance on frequency. It did have a potentiometer adjustment for voltage. Once the voltage was adjusted to ~240V, the ECM motor kicked in and ran without a problem. Hope this simple fix helps someone.


For a new issue, I suggest you start a new thread. This thread was resolved 8 years ago.


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