I have a Trane AC/Heat Pump with a non-programmable Honeywell T8411R
Thermostat. I am thinking of purchasing a Programmable Honeywell T8611G2028 model (on EBay). Is this a compatible unit? Are all the wires that come through the wall to the T8411R complete to wire the new unit so it will work properly.
Thank you, Chuck

Go to Honeywell website, and see if you can find the wiring diagrams for each. If you can save them and get back here with them.

Without the diagrams, it will be difficult for anyone to tell you if they are compatible.