Lennox G23Q3/4-100-2 And Ecobee4

Question

**Pictures attached to go along with my rambling explanation

I have my Lennox G23Q3/4-100-2 natural gas furnace and my central air system that has been working since 1995 on a basic programmable thermostat and before my purchase of a new Ecobee4 thermostat, I verified that I had a connection on the C terminal. I have 4 wires running to my thermostat, I noticed that the C terminal is actually connected to the Red wire leading to my A/C Compressor and the White wire from the compressor connects to the Blue wire going to my thermostat and connected to the Y on my old thermostat, and my Y post at the furnace has nothing connected to it. So I am a bit confused as to why the C post is connected to the Y on the thermostat, and how I now wire it to my ecobee4.

My picture show the wiring that allows the Ecobee4 to manage the heating, but no A/C, and I'm afraid to start swapping the C and Y wires around out of fear for burning out the board/compressor/thermostat or just not providing the necessary power. Ecobee4 provides a Power Extender Kit (PEK), but with my current wiring, I am not sure how to use the PEK.

Can anyone offer any advice to get my Ecobee4 working with my Lennox furnace?

Answer 1

It has hard to see that mess of wires. I believe what they did was wire nut the C to the wire that goes out to the outdoor unit contractor. That works fine as long as the blue wire is hooked to Y on the thermostat. The blue was your Y wire for cooling. But then what do you use for common?You are going to need 5 wires from your thermostat to your furnace. Just hook up R to R, W to W etc. then on the C and Y terminals at the furnace you will attach the red and white wires coming from the compressor so you will have 2 wires on each of those terminals.