No Cold Air from Central A/C - Possible Thermostat Problem?

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Old 07-16-15, 10:33 AM
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No Cold Air from Central A/C - Possible Thermostat Problem?

I've been posting on another thread about some duct work that I think has a hole in it, but now I have a new problem - no cold air from the a/c.

Our central air conditioner stopped putting out cold air last night about 11PM. The air was cool but not cold. We reset the breakers both inside and out with no luck, and then as a "let's try anything" maneuver replaced the batteries on our Honeywell thermostat. The thermostat had been acting weird with temperature reporting, saying 75 one minute, then 79 the next, then back to 75, and we didn't know why. But the low battery indicator wasn't on so we didn't even think of batteries first.

We changed the batteries and the a/c condenser came on again, and the temperature variations stopped. However, about 10AM, I noticed the a/c isn't blowing out cold air again. It's cool-ish air, but definitely not cold. Sometimes we get a burst of cold air but not all the time.

Now the thermostat is reading a steady temperature at 77F but the thermometer we have a couple rooms away is saying 81F and rising.

I'm thinking the thermostat is the problem. We're not noticing anything else (no frozen areas on the a/c unit inside, nothing weird looking outside as far as we can tell) but if you have suggestions, we'd be happy to check.

Our thermostat is a Honeywell TH3110D1008, by the way.
 
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Old 07-16-15, 11:10 AM
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Is the outside unit running when the air isn't cold? If you are suspicious of the thermostat and want to try bypassing it, remove the thermostat from it's mounting plate and temporarily jumper the wires going to the R, G, and Y terminals (connect R to G & Y). R is the 24VAC power, G activates the blower, and Y activates the outdoor unit. If you get cold air with the R,G,Y wires connected, then your thermostat is the likely problem. If you still don't get cold air, then it's likely something else wrong.
 
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Old 07-16-15, 11:17 AM
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Yes, the outside unit is running fine, though I don't think the condenser is running. It doesn't sound like it, at any rate.

I'll try jumping those wires and see what happens, thanks for the suggestion.
 
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Old 07-16-15, 11:23 AM
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I suspect you mean that you think the compressor isn't running outdoors. There are 3 main components to the outdoor unit: the compressor, the condenser (finned coils on sides of outdoor unit), and the condenser fan (on top of unit). You can easily see whether the fan is running, however you can't "see" the compressor run, all you can do is listen for the distinctive sound that it makes when it runs. When the outdoor unit is running, feel the larger of the two copper lines going to the outdoor unit (usually has insulation on it). The line should be nice and cold.
 
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