Okay, so I have been reading through many posts across sites and going over the schematics for the current thermostat, furnace wiring, and Nest learning thermostat that I plan to install. Based on what I have read and understand, I have a dual fuel system (gas furnace with electric?) that may be set up as 3H/2C dual fuel. The furnace model is a XV90 and the heat pump is XL19i. My current Trane thermostat has the following wires: R, O, Y, G, B and Y2, F, X2, W1, S1, and S2. I gather that B is actually C (common), S1 and S2 are the wires for an external temperature sensor, and that X2 would be for emergency heat. I am guessing that F is for a sensor light but not 100%. So, to wire it up correctly, does X2 go to E, and leave F, S1, and S2 taped? Also, under the custom configuration, would I then set it up as dual fuel, propane? Asking since I have seen some variation on the wiring at the furnace side and few thermostats with F, X2, and S1/S2 wired.
