Bad Thermostat Placement?

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Old 08-06-14, 08:02 PM
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Bad Thermostat Placement?





TL,DR;
I think my thermostat Is in a bad location.

Sit back, this is gonna be a long one, I say thank you and I would like to apologize in advance for the long read.

I don't know much about A/C systems, so I have included a picture of the panel on the condenser unit outside.
I have a media filter that goes after the standard filter @ the return air. The house is about 2 1/2 years old. I had a Honeywell Prestige thermostat. System ran great since we moved in to the house, new construction. We ran it at 74 most of the time.

About 3 weeks ago my house had gotten up to around 87 degrees, the fan was running constantly but the temp was just climbing. So I called an A/C repair guy and he told me to turn the system off and to let just the fan run for a while, and see if that didn't remedy the situation. 2 Hours later it had started to cool down finally. Two weeks later it does the same thing. So I called him back and he told me to do what I Had done before and he would be there shortly. He came out and looked, apparently I had gotten lazy with the filters and they both needed to be changed. He then checked the coolant levels and said they were where they needed to be. So we kicked the system back on and waited about 5 min and he checked the temp at one of the supply vents then at the return, and said that the numbers weren't quite what he was looking for, but figured it was cause we had just turned the system on. He mentioned that he thought the a/c might be getting choked out by having both filters and suggested i run with just the media filter for a few days to see how it went, if it did it again, try the standard one, then if that didn't work, call him back.The system cooled down later that night and did good for a day. Then my wife cooked dinner and the temp on the thermostat shot up to around 80 again, and stayed that way for about 6 hours. So i took out the media filter and ran the small one, cooled down, ran good for about a day. Same thing, @ dinner time the temp shot up, took about 5 hours to cool. At this point I'm getting desperate. So the next day I get home and it's at 80 again, so I went to the store and bought a cheap $20 Honeywell digital thermostat and made the change. This time the system cooled down to the 72 i told it to go to in about 45 min. I had also purchased some little wall thermometers to hang in different places in the house. Ran good for about 2 days, then my wife decided to bake a chicken. Thermostat shot up, but the thermometers i had placed around the house were reading 74. So now I'm here and my questions are as follows:

1.) Is the thermostat too close to the Oven?
2.) I know it's best practice to put the thermostat close to return air, but is it necessary?
3.) How long should the blower run after the outside condenser has shut off.
4.) what all would be involved in moving the thermostat if needed/possible.
5.) What other options can I do to remedy this.

Again, thanks if anyone read down this far.
 
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Old 08-06-14, 08:53 PM
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Welcome to the forums.


If the thermostat is in the kitchen and the kitchen gets to 80 degrees the A/C will run non-stop and your house should be cold. The thermostat is not your problem here. I'm tempted to say you have an airflow problem. Possibly the air handler needs to be cleaned.

You can measure how well the A/C is working by measuring the air coming out of a supply register close to the air handler and subtracting the temperature of the air entering the return.

You also need to see if the outside condensor..... fan and compressor..... are running all the time or are short cycling.
 
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Old 08-06-14, 09:07 PM
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Before worry about the location of the T-stat, as mentioned let's get some basic numbers first. Run the AC with only the standard filter, What is the Delta-T (the difference between the incoming cold air temperature and the return air temperature) ? Also hand feel the 2 pipes outside near the condenser, are they Warm ? Hot ? or Cold ?
 
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Old 08-11-14, 05:04 PM
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^T from supply to return is +10 degrees. I felt the pipes outside, the one under insulation is a little cool with some cold condensation on the outside of the pipe, but inside the insulation, if that makes sense. Then non insulated line is about the same as the outside air temp. Did not have the oven on today. Temp at thermostat is showing 76, it is set to go to 74, Condenser fan and blower are running non-stop and temp isn't going down
 

Last edited by skfan6; 08-11-14 at 05:56 PM.
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Old 08-11-14, 06:15 PM
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Delta T 10 is too small. should be some where between 16 and 20. and the large pipe should be ice cold. Make sure the filter and coil is clean, if you still have the problem, you need to call an AC tech to check the refrigerant level.
 
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Old 08-11-14, 08:52 PM
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Filter is clean, had only been in for about 15 days, went ahead and changed it out today. Which coil are you referring to? Tech has already came out and checked the levels and said they were good.
 
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Old 08-12-14, 06:13 AM
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Both outside condenser coil and inside evaporator coil. The AC tech should not leave a deltaT 10 system running and do nothing. If coils are clean, call the AC tech back and tell him you want Delta T 16.
 
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Old 08-12-14, 08:14 AM
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The condenser coils are clean. I had looked at my system in the house, it didn't look like there are any screws around where the coils are supposed to be. A friend at work told me he had to cut into the box that had his coil, making a door. Does that sound correct?
 
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Old 08-12-14, 08:52 AM
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Yes, some of the air handler does not have door or removable panel and you need to cut an opening. make sure you check the dirty side (air incoming side).
 
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Old 08-12-14, 10:17 AM
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Mine is an upright system, would I be correct in assuming that the dirty side is going to be the side facing towards the return air vent? Do you have a particular brand of the foam cleaner to use? Can it be used for the condenser and the evaporator?
 
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Old 08-12-14, 10:43 AM
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Yes, dirty side is the one facing the return air vent. Any soft brush will do, just don't damage the fins. (Home Depot has coil cleaner spray, can be used on both coils, that may help). Since your system is only 2.5 years old, if you kept the filters clean all the time, then I bet your coil is also clean. So the problem is probably still the refrigerant level.
 
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Old 08-13-14, 08:02 PM
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Tech came out and said refrigerant levels were good. I'm going to attempt to inspect/clean the coils this weekend. So far this week, other than Monday, the system has been running fine.
 
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Old 08-14-14, 08:05 PM
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First off, you asked questions.

1.) Is the thermostat too close to the Oven? No

2.) I know it's best practice to put the thermostat close to return air, but is it necessary? Yes!

3.) How long should the blower run after the outside condenser has shut off. Relative. Some people turn on the fan when they get home and off when they leave. Some stats have options for 30/60/90 extra runtime in heat or cool. Personal preference.

4.) what all would be involved in moving the thermostat if needed/possible. Turning off the power to the system. Cutting hole in walls. Moving the stat, and pathing holes/painting.

5.) What other options can I do to remedy this. Find the problem and fix it.

Now to the problem itself.
It sounds to me that you outdoor unit is shutting down for some reason, and you need a new tech.

When the house is warming up is the outdoor unit running?

A good service company will leave you with a report. Pressure, temps, volts, amps, superheat, subcooling, and Delta T.
 

Last edited by Jarredsdad; 08-14-14 at 08:09 PM. Reason: Grammer
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