Air conditioning kicks on in sub-freezing weather?

[Jeff Ivers]

I have a Trane heat/air unit in my upstairs controlled by a Trane thermostat. This is a unit that allows you to set the mode and the fan on automatic. If the temp gets above your upper temp setting, the air conditioning kicks on. If the temp gets below the lower temp setting, the furnace kicks on. I have had this for several years and love the convenience, because I don't go upstairs that often and the weather around here goes through some pretty wide temperature swings. I keep the limits set at 72 and 77. So yesterday, I go upstairs to wrap Xmas presents and it feels really chilly. Thermostat is reading 65 and cold air is blowing. Checked the temp settings and the auto settings and everything was normal except the air conditioning was blowing. Took it out of auto mode and put it in heat mode and got the temp back to normal. Has the auto mode gone out on the thermostat or am I looking at some other kind of failure?

 

[PelicanPines]

I winterize the outside units (3 of them). I cover them with tarps and yank the breakers. My whole system is also completely automatic. I guess I'm old school. I come from a generation that "covered" the airconditioners in the winter.

That said. It appears you have a short in the thermostat wires. I have had thermostats FAIL and do weird **** in the past. It's why I have all touch panels now.

 

[danski0224]

Likely thermostat failure or a failure in the wiring between the thermostat and air handler/furnace.

 

[Jeff Ivers]

Thank you for the replies. I had originally placed a call to the service tech for my furnace not heating. I will amend that to point them in the direction of the thermostat/wiring and hopefully that will reduce the repair bill.

 

[fitter30]

If u need the cooling either a economizer that brings in outdoor air or a condenser fan control, wind guard and crankcase heater.

 

[Milton Shaw]

Are these heat pump units, if so you might have a problem starting with the reversing valve , that is what switches between the heat and cool cycle when it's operating right. Some system default to heat when the reversing valve is not powered and some to cool when it is not powered. You have to set this up when you install a new thermostat. But is nothing has been changed then like I say it's the reversing valve starting to malfunctioning. Disregard this if it's not a heat pump.

 

[Jeff Ivers]

Are these heat pump units, if so you might have a problem starting with the reversing valve , that is what switches between the heat and cool cycle when it's operating right. Some system default to heat when the reversing valve is not powered and some to cool when it is not powered. You have to set this up when you install a new thermostat. But is nothing has been changed then like I say it's the reversing valve starting to malfunctioning. Disregard this if it's not a heat pump.

These are not heat pumps. Conventional natural gas furnace and electric air conditioner. With the thermostat set on heat mode instead of auto mode, all is well for the time. The issue for me is that in spring and fall the temperature fluctuations can be so dramatic that one needs furnace one day and air conditioning the next. At my age, traipsing up and down the stairs to change modes every other day is a pain - for that matter remembering that I might need to go check is a problem. Thus having the auto mode working is a very nice luxury. And if it does not work and has the upstairs trying to cool while the downstairs unit is trying to heat, it can get rather expensive. Still don't understand why it was trying to cool when temp was 65 and the limit was set at 77.

 

[bonneyman]

If you suspect the t-stat wiring - and it's old - perhaps you might install a wireless thermostat. I've not been a fan of those but a t-stat wiring issue could tought to track down if the wiring isn't removeable for inspection. I've had many jobs over the years that had frayed/eaten wire bundles that would short out occasionally and a specific function would not operate. First it was no operation of the heat pump, then it'd work but no aux heat, then power loss to the stat and the batteries went dead and losing the program. No rhyme or reason - really frustrating. Wasn't until I yanked the wire bundle out to find that about 4 or 5 feet in rats had gotten to the bundle and eaten all the insulation off. Five or six bare wires that - with slight movement - would short out against different other wires.
We didn't have wireless thermostats in those days but if I was doing HVAC now I'd be installing them like crazy here with all the packrat problems.

 

[KenC]

I have a Trane heat/air unit in my upstairs controlled by a Trane thermostat. This is a unit that allows you to set the mode and the fan on automatic. If the temp gets above your upper temp setting, the air conditioning kicks on. If the temp gets below the lower temp setting, the furnace kicks on. I have had this for several years and love the convenience, because I don't go upstairs that often and the weather around here goes through some pretty wide temperature swings. I keep the limits set at 72 and 77. So yesterday, I go upstairs to wrap Xmas presents and it feels really chilly. Thermostat is reading 65 and cold air is blowing. Checked the temp settings and the auto settings and everything was normal except the air conditioning was blowing. Took it out of auto mode and put it in heat mode and got the temp back to normal. Has the auto mode gone out on the thermostat or am I looking at some other kind of failure?

Does your Tstat have a battery? If so a low one can cause weird stuff. If not, ignore me.

 

[Jeff Ivers]

Wireless is a good suggestion if the problem is not in the thermostat. Everything has run just fine for the past two weeks with the thermostat in the "heat" setting as opposed to "auto". I don't think this thermostat has a battery, but I probably need to find the instruction manual and check.