Question: When installing the new thermostat I found that my new wire designations do not match up with my old thermostat's wire designations. The Honeywell installation guide provide less common wire designations but I still can't match them. My old Thermostat (Lennox) has Y,M,F,V and R but the new thermostat has G,W O/B, Y, R, and Rc. I believe I have some of the old designations hooked up correctly (F-G, V-R, R-Rc) but now sure where to hook up the Y and M. The Honeywell guide provides no insight what to do with the M wire.

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Originally Posted by raven25

Question: When installing the new thermostat I found that my new wire designations do not match up with my old thermostat's wire designations. The Honeywell installation guide provide less common wire designations but I still can't match them. My old Thermostat (Lennox) has Y,M,F,V and R but the new thermostat has G,W O/B, Y, R, and Rc. I believe I have some of the old designations hooked up correctly (F-G, V-R, R-Rc) but now sure where to hook up the Y and M. The Honeywell guide provides no insight what to do with the M wire.

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Look under Lennox on the attached diagram.