I have a newer HVAC unit that was installed using only 2 wires to control the heating only on the unit. The unit is capable of having AC connected and I would like to wire it so that it will work with my new Honeywell Wifi Thermostat AND be capable of having the AC hooked up at a later date.
I think i know how to get the G, W, R and W wire hooked up, but i dont know where to put the blue wire? can anyone help?
This is the existing thermostat how its currently connected:
This is the existing wiring diagram that came with the Heating Unit:
This is how I believe it needs to be hooked up when i install the new 5 wire HVAC Cable, I am wondering how to install the 5th wire to the system to work with the wifi theremostat?:
Best Answer
Land the blue wire on the "COM 24V" terminal
The typical use for a blue wire is to provide a C wire so that the thermostat can have constant 24VAC power available to it (saves money on batteries); as a result, simply land your blue wire on the terminal marked "COM 24V" on the control board.
As to the rest of the wires you depict? The green wire indeed goes to G, the yellow wire to Y/Y2, and the red goes to R just as you show, but the white wire needs to go to W/W1 not W2 for your single stage system. Your revised diagram, though, is correct, and so is your thermostat wiring, assuming it is configured for a conventional system (not a heat pump).