A/C unit keeps running after it reaches set temp

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  #1  
Old 06-15-12, 12:38 PM
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A/C unit keeps running after it reaches set temp

My g/f and I just moved in to a Townhome (appx. 1060 sqft) a couple months ago. About a month ago, we noticed that the a/c would keep running even though the set temp had been reached and beyond. The first time we noticed it, the thermostat was set to 77 and the temp read 75. When we bumped the thermostat up to 78, it shut off. This happens most of the time the a/c runs. Occasionally it will actually shut off once the temperature is reached.

I thought maybe it was the thermostat they had installed (simple digital one), so I replaced it with one we had purchased for our old apartment but unfortunately, it still does it.

We also have hardly ANY airflow upstairs (we just purchased a window unit and use that at night).

Unfortunately I'm at work, so I can't provide any model numbers right now, but if anyone has some suggestions as to what my problem might be or what I can test myself to narrow it down I'd appreciate it.

Thanks in advance
 

Last edited by davids80; 06-15-12 at 12:55 PM.
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  #2  
Old 06-15-12, 02:39 PM
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You just have the one thermostat?
 
  #3  
Old 06-15-12, 09:19 PM
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If the t-stat is mounted on an exterior wall, plug the hole behind it.
 
  #4  
Old 06-16-12, 06:25 AM
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regardless of where it is mounted plug the hole behind it.
 
  #5  
Old 06-18-12, 07:15 AM
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Was a bit busy over the weekend, so I didn't have time to check this post until today. Yes, I only have the one thermostat (and one unit) for the upstairs and downstairs. It's not mounted on an exterior wall, in fact, it's mounted on the wall to the left of the a/c unit:

thermostat ->[|_a/c_|

Hope that makes sense. Anyway, what should I use to plug the hole behind it?

Oh, one other thing. Not only is it running past the set temp, but it doesn't come on right away when it get's warmer than the set temp. Ex: Set to 77, reads 78, not on. Have to manually turn it down to 76 to get it to come on, then back up to 77. At which point it will probably cool it to 76 or 75 before it shuts off on it's own.

I really don't think it's the thermostat since not only was the old one that came with the place doing the same thing, but the newer one I installed 1) is only about 2 years old. and 2) worked perfectly in the old place.
 
  #6  
Old 06-18-12, 09:17 AM
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Replace your thermostat...
 
  #7  
Old 06-18-12, 09:35 AM
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Not a pro - but don't some thermostats have a cycle rate to keep the AC from turning off and on too much ? I would think a two degree swing would be somewhat normal.
 
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Old 06-18-12, 09:56 AM
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I know mine allows me to set the sensitivity - I can set it to kick on and off when it's 1/2, 1 or 1 1/2 degrees from the set temperature. Three degrees seems pretty extreme.
 
  #9  
Old 06-18-12, 10:34 AM
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mitch17: I don't think ours has that setting, though it does hav an "econ" mode that will kick on if the set temp is more than 5 degrees away from the actual temp, and all that does is let the unit gradually reach the set temp instead of running non-stop to reach it.

tribe_fan: I thought that too, but considering it's running 10+ minutes after reaching the set temp, I don't think that's what the issue is.

hvactechfw: Do you have any recommendations for replacements? Do I need to use anything specific to plug the hole behind the thermostat? It's only about an inch in diameter where the wires come through.

Also, what reason(s) are you thinking when you suggest replacing the thermostat? I'm only asking because two completely different thermostats are having the same "problem".

edit: This is the current thermostat we're using
 
  #10  
Old 06-18-12, 02:04 PM
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According to your manual (page 41) the default setting is 1 degree either way, but can be adjusted.
Would it take 10 minutes to raise the temperature 1 degree?
I also think the TStat has a delay built in - see page 48. I thought my TStat was broke until I read my manual - (didn't know about the 3.5 minute delay !!)

http://www.hunterfan.com/uploadedFil...oads/42711.pdf
 
  #11  
Old 06-18-12, 02:58 PM
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Thanks for that tribe_fan, I didn't know I had that option. In all honesty, my g/f was the one who set up the programs and such after I installed it, so I never bothered to look that far in to the manual lol. I'll try adjusting that when I get home and post back with results.
 
  #12  
Old 06-18-12, 04:40 PM
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Hunter makes great fans, not thermostats. Buy a honeywell rth7600 or a pro series.
 
  #13  
Old 06-19-12, 05:30 AM
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So when I got home last night, I started telling my g/f about what you found tribe_fan, and she hopped up off the couch and says "I know what he's talking about!". Checked the span mode and sure enough, it was on 3. We have no idea how it got there since the default is 2, she hadn't touched it (forgot about it until then) and I didn't know that option was there. Either way, set it down to 1 and it's operating perfectly! Thanks again =)

Oh and hvactechfw, thanks for the info. I'll keep those in mind whenever I do have to replace this one.
 
  #14  
Old 06-19-12, 08:11 AM
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She knew what you were talking about, but never touched it?
Sounds like my wife lol. (maybe you got a returned one?)
 
  #15  
Old 06-19-12, 12:30 PM
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I don't think it was returned.. package was sealed (wouldn't have gotten it if it wasn't). Weird thing is is that it worked perfectly when it was installed at our old apartment for two years. Maybe it got "changed" when I put new batteries in it. The manual said it reverts back to factory setting (which is 2) when the batteries are replaced.. who knows? I'm just glad it's running like it should. Hopefully the power bill won't be as high next month.

Thanks again everyone =)
 
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