I have a Honeywell RTH230B thermostat connected to my 4-wire system. I replaced my old Honeywell Mercury thermostat last fall.

I just checked my wiring, and I have Green to 'G', Red to "Rh" (jumper is present), White to 'W', and Yellow to 'Y'.

I used the furnace all winter without any issues, but now that it is time to use the A/C, I am having the following issue:

When set to Cool, the furnace comes on (flames are burning), and blows hot air.

:mad:

Your color code is correct. The wiring must be wrong at the furnace or you have a defective thermostat. Note try removing the white wire and see what it does..

Your color code is correct. The wiring must be wrong at the furnace or you have a defective thermostat. Note try removing the white wire and see what it does..

Thanks... everything works great! Although, I was hoping I didn't have to Jerry-rig it.

Any thoughts on what I'm looking for as far as bad wiring in the furnace?

My thoughts are as follows. The low voltage wiring color code is not to standards. You are going to have to track down each conductor and see where they go. Then change the problem with two of the wires.