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Heating, Air Conditioning, Fridge, HVAC/Heat on when calling for cooling.


Hi Jim,
I have a 8yr.old Trane split-system a/c with a 12 yr. old 90%Lennox gas furnace.  I replaced and relocated my tstat last year due to the old one was low quality and located where it was getting late afternoon sun as well as in the way of some sconce lights I was installing.  The new tstat wire was installed with the furnace power off and almost the whole run is visible from the basement so I know it's not snagged on a screw or something.  Since I replaced the stat the heat comes on with a call for cooling.  The wires ohm out ok, the new stat is sending 24v through G and Y.  I triple checked all wire connections and they're good and correct.  I went ahead and replaced the ignition control board thinking that it couldn't be anything else, to no avail. I am at a loss on this one.  I appreciate any additional troubleshooting hints or something that's right in front of me.  Another setr of eyes always helps.  Thanks so much.

Hello David,

The best thing we can do is start with the basic's. Yellow on stat lands on Y. Yellow wire goes to the furnace and is wired to the yellow wire going out to the condensing unit. The yellow is landed on Y. Make sure no other wires are connected to this circuit.

The white wire to the stat is connected to W. The white wire in the furnace connects to W.
I know you have checked this but look one more time.

When you switch to cool does the furnace and the condenser come on at the same time?

Let me know.

Heating, Air Conditioning, Fridge, HVAC

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Jim S.


I can answer questions on gas or electric furnaces, ac units and heat pumps. I don't work on boilers,chillers,or home appliances.


I have been in the HVAC trade for over 35 years. For the past 15 years I have owned my own business. I am semi-retired so I can answer questions in a timely manner.

I attended trade school for 5 years on weekends and evenings. This was very hard to do, but well worth it!

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