# Central Air Conditioning running all day



## quaildog (Mar 12, 2011)

I'm writing to see if someone can answer my questions regarding
central air-conditioning or refer me to someone who can. Our new central air conditioner runs all day and the company that installed it says that it's normal.

We live in a 14-year old R-2000 certified home in the country. The house is approx. 1,500 sq. ft per floor and there are a number of large argon-filled windows. After getting a number of quotes,
we chose Sears to install a 2-ton, 14.5 SEER unit in June 2010. Once we started using the unit, we noticed that it was running all day. I started keeping notes and found that it would typically
start around 9:30 in the morning and run all day if the temperature outside was anywhere above 27 degrees Celcius. The thermostat was set to 22 degrees Celcius. The company salesman came and measured the house to ensure we had the right size unit and he had their service people check the system out as well. Finally, the company service manager spoke to the manufacturer who replied that these new types of air conditioners focus more on the humidity and will typically run all day. The temperature in the house might even go up slightly in the afternoon depending on how
high the temperature gets outside. (I had central air in a previous house 20 years ago and if I turned on the AC when I got home from work, the house was cool within a few hours at most.)
The service manager told me that I wouldn't be able to get an AC to operate the way I wanted. Getting a larger unit wasn't recommended either because the fan and ducts might not be able to handle it and the AC coil in the furnace might freeze up completely.

My question is this - is it now typical for today's new AC units to run 10-12 hours a day without stopping or am I being fed a pile of baloney?

My basement ducts are already all closed. Is there anything else I can do?

I find it hard to believe that the AC must run all day, even when the temperature is below 30 degrees Celcius!


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## yuri (Nov 29, 2008)

Pure balogna. Probably neither the tech or the service manager know how to properly adjust the freon level and check the unit properly. Probably is low on freon and may have a freon leak. It will damage the compressor from being low on freon so you need to get it fixed ASAP. Your house is the same as mine in size and better insulated and my 2 ton unit runs 20 mins ON/40 mins OFF in 30 deg C weather. Big box stores and S***s use sub contractors and the lowest bidder gets the jobs. I work for the highest bidder who pays the highest wages if you get my meaning. May have to get another reputable co to check it and make a report. Then contact Sears if it does not get resolved then the BBB and then Sears. Finally go after the manufacturer if necessary. They don't want their products to get a bad reputation. The service manager is lying when he said the manufacturer told him that. That is a blanket statement for hot humid climates like Florida where the units run longer to remove humidity. We also downsize some of them too run longer and remove more humidity ONLY if they were oversized in the first place. For a few bucks you can do your own heat load calculation and verify you have the right sized unit. Then they cannot argue with you over the sizing.
Load Calculator


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## Doc Holliday (Mar 12, 2011)

BS. Units are specifically designed to cycle on and off, dehumidifaction included. Never are they to run continuously, not even if set on low speed during cooling for dehumidification when in fact on variable speeds they can be set to "ramp up" in speed from a low speed for some variable amount of minutes for dehumidification to full speed after dehumidification and then shut off when desired set point is reached and repeat, called cycling. Again, on and off and on and off, never always on as that in itself defeats energy efficiency.

Is this only the condensing unit you had replaced or are we talking the entire system meaning air handler (with evaporator coil in it) and condenser or furnace and individual coil and condenser and what was your old system size?

If you have any of the old system's model and/or serial numbers it would help.


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## hvactech126 (Nov 11, 2010)

it sounds undersized or undercharged, but there are questions we need answered as in the last post. Was a heat load calculation done?


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## cturman (Jun 7, 2010)

The system may be a bit small but that is usually a good thing. A few questions. 

Dose it keep the house comfortable?
What was the outside temp? 
22 seem a bit low for me. I keep mine at 78 or 25 in the middle of the day and this is quite comfortable. 
What is the temperature of the air coming out of the vents and what is the temp going into the return?
Finally was your electric usage higher than expected?


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## heatycooly (Mar 11, 2011)

For your sizehome you need at least a 2.5 ton probably a 3 ton it is undersized the freon levels are probably right but if its too small it won't shut off


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## beenthere (Oct 11, 2008)

New units tend to do a poorer job of dehumidifying. So who ever said the manufacturer said that, fed you a line. It sounds under sized.

On a design day, the A/C should run continuous. Do you know what your outdoor design temp is?


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## AllanJ (Nov 24, 2007)

If you manually turn it off (raise the thermostat temperature setting) every hour for a half hour, does the house not get cool enough?

If the system runs almost continuously on a slightly hotter than normal day and does not cool the house enough on a quite hot day then the system is undersized or needs service (Freon, etc.).


beenthere said:


> New units tend to do a poorer job of dehumidifying.


The system has to be designed to get the proper range of air temperatures at the coil outlet. Generally, the lower that temperature, the better the dehumidification achieved. But if the air temperature at coil inlet together with the volume if air passed are both too low than the coil freezes up. A less sophisticated system may not control the air flow that precisely usig varialbe blower speed, etc. To make up for that and prefvent freeze ups the outlet air temperature is allowed to average higher. Then the system has to run longer for dehumidification's sake. It still stops at the target temperature leaving the humidity a little higher than a better system does for that temperature. The occupants then set the thermostat a little lower and, provided the system is able, everyone is happy.


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## beenthere (Oct 11, 2008)

AllanJ said:


> If you manually turn it off (raise the thermostat temperature setting) every hour for a half hour, does the house not get cool enough?
> 
> If the system runs almost continuously on a slightly hotter than normal day and does not cool the house enough on a quite hot day then the system is undersized or needs service (Freon, etc.).
> 
> The system has to be designed to get the proper range of air temperatures at the coil outlet. Generally, the lower that temperature, the better the dehumidification achieved. But if the air temperature at coil inlet together with the volume if air passed are both too low than the coil freezes up. A less sophisticated system may not control the air flow that precisely usig varialbe blower speed, etc. To make up for that and prefvent freeze ups the outlet air temperature is allowed to average higher. Then the system has to run longer for dehumidification's sake. It still stops at the target temperature leaving the humidity a little higher than a better system does for that temperature. The occupants then set the thermostat a little lower and, provided the system is able, everyone is happy.



Newer systems tend to use a larger indoor coil that doesn't get as cold as older systems did. While you can slow the blower, down, that tends to reduce the system efficiency so that the customer doesn't get the efficiency that they paid for.


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## Doc Holliday (Mar 12, 2011)

I'd like to know what this system's target superheat was/is and what the actual super heat is. Bets as to it also being undercharged so the sh is higher than target meaning past saturation still being in the evap coil lines and beginning to pick up heat in vapor while inside coil?

Correct to slightly overcharged would mean lower sh but more capacity (of coil, ability to absorb heat from space), txv.


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## Doc Holliday (Mar 12, 2011)

heatycooly said:


> For your sizehome you need at least a 2.5 ton probably a 3 ton it is undersized the freon levels are probably right but if its too small it won't shut off


 
Can you please explain how you came to this conclusion?


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## Marty S. (Oct 31, 2009)

Could be several reasons why it runs all the time when the temp is above 80 and none of them are normal.


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## yuri (Nov 29, 2008)

Guys, he has a R2000 home with 8 inch thick R-26 walls and low e-argon windows and perfectly glued sealed airtight vapor barrier. Also has over R40 in the attic. Google R-2000 homes for more info. It is INCREDIBLY airtight and energy efficient. They do a blower door test before certifying it. I saw a 18000 sq ft R2000 home here being heated by a 60% efficient 90,000 BTU furnace. Normal home would have had 135-150,000 BTUs. 2 tons is the right size but it is obviously not setup properly. Plus he lives in a rural area with better breezes and less heat load than being crammed in the city. Probably has good shade trees also.

http://oee.nrcan.gc.ca/residential/personal/new-homes/r-2000/standard/standard.cfm


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## Doc Holliday (Mar 12, 2011)

yuri said:


> Guys, he has a R2000 home with 8 inch thick walls and low e-argon windows and perfectly glued sealed airtight vapor barrier. Google R-2000 homes for more info. It is INCREDIBLY airtight and energy efficient. They do a blower door test before certifying it. I saw a 18000 sq ft R2000 home here being heated by a 60% efficient 90,000 BTU furnace. Normal home would have had 135-150,000 BTUs. 2 tons is the right size but it is obviously not setup properly. Plus he lives in a rural area with better breezes and less heat load than being crammed in the city. Probably has good shade trees also.
> 
> http://oee.nrcan.gc.ca/residential/personal/new-homes/r-2000/standard/standard.cfm


 
Hence superheat.


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## yuri (Nov 29, 2008)

I am sure it is not setup properly. He had a older 10 SEER unit and they did not adjust the fan speeds and superheat etc with the new unit. I would like to know if he bought a new furnace with it. Obviously he appreciates quality and has a few $$ to spend if he paid $10-20,000 more for a R2000 house. If it is a new furnace with variable speed drive they probably left it going full blast for 5 tons of cooling capacity with the fan. Happens all the time.


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## heatycooly (Mar 11, 2011)

Well I have been in the business for quite some time and I have also sized many units I can't do a load calculation obviously but from what I've read it sounds too small


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## quaildog (Mar 12, 2011)

Thank you to everyone who has offered their suggestions. I thought I would provide a bit more info because of them.

My home has R40 walls (10 inch) and R60 in the attic. The central AC unit was a new unit installed last June into my existing electric furnace. (Before that, we didn't have central AC, we were using two portable AC units only.) The unit is a 2-ton Kenmore 77410 Series with a SEER of 14.5 and 2-speed fan. I was told that my Nortron electric furnace and ducts might not be able to handle a 2.5-ton unit since the coil in the furnace might freeze up. The furnace is not new but has hardly been used since I heat with wood. The electric furnace was our back-up. We have a prevailing north-west wind so our windows were usually open whenever possible during the summer. I have noticed in some of my recent readings that the outside unit should preferably be installed in a shady area. However, my unit is installed in a full sun area on the south side of the house.

The unit would typically run continuously whenever the temperature was 28 degrees celcius or above outside. However, by suppertime, the house was usually comfortable and cool.

A Sears service technician came out last July and measured the air temperature difference between the in and return sides of the unit - it was about 11 degrees Celcius. His only other suggestion was to stuff T-shirts in my basement ducts so that all the cold air was sent upstairs. In August, the salesman came out and measured all the rooms and windows and later confirmed that my AC unit was the proper size. Sears then sent their most senior tech and he found the unit was a bit low on freon and topped it up. He also measured the temperature difference and I believe it was around 12 or 13 degrees Celcius difference. The furnace fan is also running on its' fastest speed. When the service manager told me that the manufacturer had told him they were meant to run continuously in hot weather, I asked for his number and called him directly. He repeated what the service manager had told me. Apparently today's AC units have smaller compressors to save on energy although they do work much longer.

By suppertime, as long as the outside temperature wasn't in the mid-30's, the house would be cool but the unit kept running. I would typically turn it off in the evening.

I've tried to compare my electricity bills but it hasn't been easy since I was using portable AC units and fans at times before and the price of electricity has increased quite a bit here. We live outside of Ottawa.

I have a Hunter Energy Monitor II programmable thermostat which I've had for about 15 years. Someone told me that some AC's have problems with some of the older programmable thermostats. Maybe I'll try a new one in the Spring and see if it makes a difference.

Someone suggested I try setting the unit a bit higher. This summer, I am going to try setting the unit to, let's say 21 degrees, so it'll start earlier in the morning, then increase the setting to say, 23 or 24 degrees at 10:00 AM to see if that makes any difference in the run time.

Thanks again to all for the comments and suggestions.


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## yuri (Nov 29, 2008)

Ottawa can be pretty humid so that adds to the work load. Part of your problem has to do with the way you are running the unit. I would NOT use a setback program in Canada. I tell all my customers to set it at 22 and let it run all the time unless the weather changes and you know it is going to be cool (under 20 C for a few days). The units are designed to safely run continuosly and if you were getting 11 C supply which is 50-55 for the US guys then that sounds reasonably OK to me. If you let it start in the morning it will progressively remove the humidity (which you have more than me) and it will work better. As this is your first AC you have nothing to compare to. I think it is the right size and you do need to keep NO cold air going into the basement. Your Nortron should have a max 3 ton blower so it should be OK. The trouble with internet troubleshooting is we don`t always get all the necessary info in the beginning. I would still get another checkup from a experienced tech to make sure. Not all the big box subs are poor quality but a lot are so a second opinion is a good idea. A new Honeywell Focus Pro thermostat from HDepot or Rona will work better than the old one you have now and save you energy $$ by being more sensitive and accurate. Hopefully you have drapes or blinds for your windows. I have low e-argons but the best one is around a R4 so drapes and blinds are still required.


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## Doc Holliday (Mar 12, 2011)

okay, now we're getting somewhere. The 2 ton is officially equipped with a 1.5 ton compressor so that is your system size, not 2 ton. It is true that newer systems are built like that, not all but most. So in essence the sales guy said that your ducts are spec'd for 1.5 ton and a 2 ton compressor (in a 2.5 ton unit) not will work as per your ducts even though blower speeds can be manually set..? Now we need to know duct size to calculate cfm to see how far you chain is being pulled and I'd have to still think it's quite a bit, from this end only though as I'm not where you are or familiar with systems running all day. never heard of that before.

you should be able go a bit bigger and add a duct to or two or replace existing (if any duct needs work/replace/upsize to begin with hence cfm and size of ducts)/upsize and for not too, too much cost so there are many ways around that.

The main thing here is your comfort.


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## yuri (Nov 29, 2008)

Losing a 1/2 ton of cooling. Afraid not. Lots of them are 22-23-24,000 BTU compressors but never a 1/2 ton lower. Quaildog here is some engineering specs for more info. see p.5 KBthu = 1000s of BTUs /hr and a 2 ton unit is 24,000 BTU/hr

It varies according to the outdoor temp and humidity but the compressor is always within 2000 BTUs of the manufacturers rating. Copeland does not make them exactly 2 ton and in the model # there may be a 22 meaning 22,000 BTUs. A 2 ton compressor is a nominal rating which can be between 22-24,000 BTUs depending on the manufacturer.
http://tech.lennoxintl.com/PDFs/ehb_13acx_rtgs_0904.pdf


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## beenthere (Oct 11, 2008)

While the compressor may be rated at only 18,000 BTUs at 130°F condensing temp, at 105°F condensing temp is will have a rating of 24,000 to 27,0000 and some odd. 

My A/C will run for 6 hours straight when its 98°F(36°F) outside(about 6 degrees above our outdoor temp design). My A/C is 8 years old.

Your furnace may not have a strong enough blower, if it was designed without an internal evap coil.


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## yuri (Nov 29, 2008)

Probably true about the blower size/capacity. 14 yrs ago Nortron would probably have put a 2 ton blower in his unit which probably is a 15 kw. The newer ones come equipped for 3 tons of cooling. If he is getting a 55 supply temp his Delta T is 15-20 deg and good. It has not froze up so it is safe to use that way. No way for us to know for sure what is going on w/o actually being there and seeing the duct size etc etc. That is an expensive custom home and I highly doubt the contractor would have skimped on the duct sizing. They don't want problems or to lose their reputation and to be a R2000 certified builder everything is done to high standards. In the cheap cookie cutter homes yes, but not in that grade of home.


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## Doc Holliday (Mar 12, 2011)

beenthere said:


> While the compressor may be rated at only 18,000 BTUs at 130°F condensing temp, at 105°F condensing temp is will have a rating of 24,000 to 27,0000 and some odd.
> 
> My A/C will run for 6 hours straight when its 98°F(36°F) outside(about 6 degrees above our outdoor temp design). My A/C is 8 years old.
> 
> Your furnace may not have a strong enough blower, if it was designed without an internal evap coil.


 
Can I ask how we figure out the btu's from the condensing temp, the equation? Thanks.


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## beenthere (Oct 11, 2008)

Doc Holliday said:


> Can I ask how we figure out the btu's from the condensing temp, the equation? Thanks.


I have info on it somewhere. But no idea where. Its basically how many pounds of refrigerant being moved per minute and how much wattage the compressor uses to move that much refrigerant. Along with the condensing temp.

However, Copeland publishes the capacity of their compressors at the different condensing temps.

A 2 ton unit using a compressor that is rated at a 105 degree condensing temp may have a total capacity of 23,000 BTUs at 95 outdoor temp, 80 degree indoor temp, and a total capacity of 24,800 BTUs at 85 outdoor temp and 80 degree indoor temp.

While the compressors are smaller in displacement/pumping capacity, the condenser coils are larger/more efficient at rejecting heat and do reject more heat from the lower volume of refrigerant, so the larger compressor is not needed.


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## Doc Holliday (Mar 12, 2011)

Is this something I'll find in my Refrigeration and A/C Technologies book?


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## beenthere (Oct 11, 2008)

Doc Holliday said:


> Is this something I'll find in my Refrigeration and A/C Technologies book?


Should be in there.


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## mastertech (Mar 14, 2011)

Hi Ive read your problem and I can gurantee you there was a step missed in replacing your system.I agree with doc holiday .If a system is designed correctly it should be shutting off.First off you said 1500 sq ft per floor.Is this home multi level. when this system was changed out,was the system done as a whole both indoor and outdoor unit.Im kinda turning towards the system sizing.Its good that you have a home with good windows and insulation.From the sounds of it you have multi levels on home and air distribution can be a factor on system performance.Id like to get some more info on this .being a system set up for an weatherization program ,was there a recognized heat load calculation performed ...manual j or other approved program?Is the air flow set up properly,how about a superheat/subcool measurement performed.theres a lot of things that make a diiference on the performance ,effeciency and the economics of a systems performance.A system to run top notch everythings designed evenly and for proper sizes to enable your system to produce the proper comfort throuhout the home with out any hot/cold spots .The home should be even temp for proper comfort level


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