My old thermostat wiring looks like this: enter image description here

So its good I have a C wire and its running on 24v. The hard thing is the fan control. It's a proprietary 3 speed fan - where do I wire those 4 wires to? What is Fan "Com"?

I plan to purchase a Google Nest Thermostat but the compatibility tool is not complete as I have MORE wires than they need for fan control.


1 Answer 1


From the Google Nest Support Page at:

Nest Support Page

Nest Multi-speed and a Fan

It's not clear what the tech will do but I suspect they have some additional hardware that controls the fan.

  • Great, have to pay another $300 for a 15 minute job
    – Kevin
    Nov 21, 2020 at 0:32

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