My air handler (see photo) connections are G,W,Y,R and COM. The a/c compressor (outside) is connected to air handler Y and COM. I have 5 wires out to the thermostat, G,W,Y,Rh with jumper to Rc, and an unused blue.

How can I connect to new Nest thermostat using the unused blue as c-wire.

Connector wiring

1 Answer 1


This is easy

Just land your blue wire on the Com 24V terminal on your air handler's control board and on the C terminal of your Nest. (Don't worry about having two wires on one terminal on an HVAC-board terminal block -- they're designed to handle that.)

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