Hello everyone,

Having a problem with my Lennox furnace. This winter out of the blue while the heat was on the A/C unit outside kicked on. After looking at it I found out that the heat would run for a few minutes and then the unit would turn on outside. This would happen sometimes and then not. Nothing was changed or worked on the system. I replaced the thermostat thinking that was it but that made no difference. I have a simple dial thermostat nothing fancy. below are the model # and Ser # if that helps. I live in the Chicago area and it is not a heat pump system. Thanks for any help in this. I have turned the breaker off to the unit outside till I figure this out.

Model# G12Q3-82-6
Serial # 2187M65089

 

What's the model of the a/c?

There's probably an issue (like a short) in the low voltage wiring.

The furnace is a 1987 and I suggest you get the heat exchanger inspected. It's probably cracked by now. https://www.youtube.com/watch?v=tIZ20EA6v04

 

Muggle I would assume the low voltage wire your talking about is from the thermostat to the furnace? That was going to be the next thing I was going to do. was run a new wire. The furnace was installed when the town-home was built in 1991. Did they have this sitting around for four years before the built the place? that would stink if that was the case.

 

Please see the above post. Thanks.

 

Check the stat terminal strip in the furnace. Make sure the Y wire is not touching any other wires.

 

yes, the issue could be in the furnace itself.

its possible that the furnace was sitting for a few years - maybe the installer got a good deal on many g12s