Central A/C Running for Long periods of time

We just moved into a house last summer. When our Air Conditioner comes on it seems to run for about an hour at a time. Does this seem right? It's 82 Degrees outside and I have the thermostat set to 75. It also seems like the temperature drops very slowly (about a degree an hour). Could this be a problem with the thermostat? It's a Hunter, which I haven't heard great things about. Our thermostat is downstairs. We have a baby monitor upstairs that shows the temperature and it says the bedroom it's in is at 69 degrees. I just don't know if it's a problem with the actual A/C or the thermostat. The air coming out of the vents seems cold.

 

You said the air coming out the vents is cold, how cold ? how many degrees lower than the room temperature at that time ? A degree per hour is a little slow. Upstair 69F is not right , should be 75F or higher.

 

What would be the best way to measure the temperature of the air coming out?

 

Take a thermometer hold 1 inch in front of the vent.

 

Sounds like a air balancing problem. Too much air going upstairs, try to find the balancing dampers.

 

Thermostat set to 74 and I measured the temp out of the vent at 58.

 

58 is a good temp. AC working properly.

 

As mentioned, the AC is fine. you should try to direct more cold air to downstair. Use damper if you have them, if not, you can close half of the registers upstair, and see if that help.

 

Thanks for the suggestions. Another bit of info is that my thermostat is in a very open area of my house (the kitchen, dining room, living room, steps and foyer are all in one open area). Could this be why it seems to take a while to cool down? At the bottom of the steps is the door to the basement (finished but not air conditioned) that I keep cracked but not completely shut.

Also, I notice my thermostat has some SPAN setting (Fast, Medium or Slow) that I'm not exactly sure what it controls, but I believe it has something to do with how often the unit turns on?

 

Unless the T-stat is near the basement door and hot air is drawn from basement, otherwsie, t-stat is an open area is fine. But that door needs to be closed. SPAN setting allow T-stat turn on or off when temp is 1, 2, or 3 degrees different from the set temperature. but the SPAN should not cause your upstair 69 while downstair is 74. Also, Is the baby monitor thermometer accurate ?

 

It was accurate last time I checked it. I wasn't so much concerned with the temperature difference as the A/C running for (what I would think) are longs periods of time and taking a while to cool down. I only mentioned it to see if it was a symptom of the problem being with the t-stat.

 

It would appear that your A/C system has some problems that you can help us troubleshoot.

This is NOT DIY > fixing anything yourself; this is merely a safe easy way to check your A/Cs nominal performance, if it is not performing near to the nominal specs you call an HVAC Contractor to FIND & FIX the problems.

There are too high a percentage of systems that are NOT performing to near their Rated nominal capacities that need addressing by a good licensed technician.

If you want to do some safe easy ways to check your A/Cs performance, you should get a 'digital air probe thermometer' that registers in tenths degrees and a low cost percent relative humidity gauge to check the indoor humidity level.

If you have an air conditioner that was manufactured between 1992 and 2005 it is a 10 or 12 SEER, R-22 refrigerant unit.

When the temperature reaches 85° outdoors and the indoor temperature is close to 80°F and the relative humidity indoors is right around 50% RH the outdoor condenser temperature split above the outdoor temperature should be around 20 to 21°F or, around 105°F.

When the temperature reaches 85° outdoors, if the indoor temperature is close to 75°F and the relative humidity is 50% then the air discharge temp-split off the condenser should be around 17°F or, 102°F off condenser.

The indoor temperature split between the return-air at the supply air grille closest to the air handler should be around a 19 to 21°F temperature drop with either an 80°F or 75°F indoor temperature. This is also the indoor split with the higher SEER units at 13 SEER or above.

If the indoor temperature split is too high may have very low airflow which needs to be brought up to its normal CFM Rate.

If the outdoor condenser split is too high your air handler may be drawing hot air into the return from the attic causing the high condenser discharge air temperature.

If the temps are within plus or minus a degree or two, that air-conditioner is performing fairly well.

On the new air-conditioning systems at 13 SEER & higher the outdoor condenser split is much lower than it is on the 10 to 12 SEER units; the indoor temp-split is the same.

Far too many HVAC service persons do not check the airflow CFM & the actual delivered performance of the system...

 

The AC won't shut down until the room temp reach the T-stat set temp. To check your T-stat, you can put another thermometer right next to your T-stat and watch their temp and see if they go up and down the same and shut donw and start at the correct set temp. There are lots of reasons that can cause AC to run a long period of time, for example, AC air is not cold enough, AC air is not blow strong enough, house is not well insulated, door/window open,etc.. So, if the T-stat is OK, you need to find out why the downstair temp does not go down fast enough. You may have to check air temp and air flow on all your registers, and make sure strong & cold air goes to downstair so that the T-stat reach its set temp fast. Since you said it goes down 1 degree per hour, that indicated your AC or house has problem. should be 15-20 minutes, not 1 hour.

 

Thermostat read 75, second thermometer placed near it said 72, and it started to feel a lot colder than that when it kept going. It's been a while since we replaced the batteries in the T-stat, if the batteries are low can it affect the way it reads temps?

 

It may or may not. Go ahead put a new battery in, and see that works, if not, you need a new T-stat. But again, the T-stat has nothing to do with your upstair cold and downstair warm problem, you still have to work on the air flow.

 

I was going by the temperature on the Thermostat for the downstairs temp, so if that is reading the temperature wrong, it's possible that there wasn't much temperature difference at all if the actual house was colder than the thermostat was reading.

 

OK, in that case, install a new T-stat, and also put a good thermometer upstair. that is all you need.

 

A good thermostat...not a $30 Hunter. Expect to spend $60-90 depending on functions. Much more if you want a fancy wifi type, that will make your breakfast each morning.

 

So I got a new Honeywell Thermostat. I turned the A/C on at 7:00 and the temperature was 78. It look about an hour to get to set point of 74 (so much better), however when it got to 74 it's not shutting off. The temperature doesn't show it going any lower but the unit doesn't shut off. Also, when I bump the temperature up to 75 manually it does shut off. Could it be a wiring problem? I attached a picture of my wiring if that helps. (It's hard to see but there is a red wire going into RC and then a bridge wire from RC to R)

 

I guess I jumped the gun. Turned it back on and it ran for about 30 mins and then shut down. Seems to be working fine now.