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Old 06-11-2007, 09:57 AM   #1
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AC Unit Continuously Runs - yet it is cooling


Looking for some AC help here.

Last week, the AC in my home began to not stop running. The unit blows cold air (it is working in that respect) but when the target temp on the thermostat is reached the air keeps running. it gets worse, the air keeps running no matter what I do with the thermostat; switch it to off or heat and the air keeps running.

So I replaced the thermostat, and get the same results. No matter what, the air conditioning runs. The only way I can get it to shut off is to flip the breaker for the unit off.

Any ideas? The unit is a Coleman and the new thermostat is a LUX.

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Old 06-11-2007, 12:03 PM   #2
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AC Unit Continuously Runs - yet it is cooling


First off, gotta ask, you do know there is a separate switch for the fan, right? Meaning, you can change one switch from "heat" to "off" to "cool" all you want, but if you have the fan switch on "on" instead of "auto", the unit will keep running. So, are you saying the fan keeps running, or the actual outdoor AC unit (condensing unit) keeps running too? Just checking.

That being said, giving you the benefit of the doubt (that the outside AC unit is what keeps running), I would guess you have a short in the wiring connections at your furnace/blower unit.... such that the low-voltage wiring from the cold/off/heat side is continually getting a call to run the AC, even when the thermostat is satisfied. And depending on what built-in safeties your system has, there must also be something wrong with those, because the unit would eventually shut off from one of the safeties (I would think you would eventually be overheating something, or freezing your coil, or something).

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Old 06-11-2007, 01:11 PM   #3
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AC Unit Continuously Runs - yet it is cooling


Thanks for the reply and the sanity check! Your right, I am talking about having the fan and unit both off on the thermostat, yet the unit outside continually runs. The only way to get the outside unit off is to flip the breaker.

Any ideas on how to check if there is a short in the wires? Any ideas on why it would have happened all of the sudden with no changes being made to anything?
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Old 06-17-2007, 05:36 PM   #4
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AC Unit Continuously Runs - yet it is cooling


It's pretty simple really, ohm it our with your VOM.

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Old 06-17-2007, 07:04 PM   #5
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AC Unit Continuously Runs - yet it is cooling


Is this unit in a Manufactured Home? If it is, and there are switches on the air handler unit, you need to only wire the Heating side of the Thermostat. If the Thermostat handles the Heat/Cool/Off & Auto/Fan settings, then make sure that you have the thermostat wired correctly. Also, was the jumper left on the Thermostat if it pertains to your Air Handler?
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