A:Answer HMMMM, I think that would be difficult. I have heat and air on one thermostat, but it was a four wire system. The Ecobee4 comes with what they call I think a power extender. The Ecobee is a five wire thermostat. With the power extender, you can use the four wires, but be careful, it can get a little tricky. I have an older furnace and no clear cut terminals like they show in the installation instructions. I had to solder the "C" wire to one side of a 24 volt output transformer in the furnace to provide voltage to run the Ecobee. Once in, it works great, though I wish it had more functionality. This probably wasn't much help for you. Sorry. If it helps, the red wire ultimately ends up going the one side of that output of that transformer. The Green wire is the one that calls for heat while the Yellow one goes to you air conditioner condenser, and the white, or black is the common.
