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Sorry for the newbie question, but I would like to hook up a C wire so that I can get a Nest, Ecobee, etc. My current thermostat is just a regular battery operated Honeywell and looking at the current thermostat wire, I have the extra blue/brown wires available, but they aren't being used and not connected to anything. I looked at the control board at the handler and there already is a wire on the C terminal going to the air conditioner condenser outside.

In the picture below - the top red (R), white (W), green (G), yellow (Y) and the unconnected brown/blue wires are going back to the thermostat . The middle white (C) and red (YR) wires go to the condenser.

I assume I need to connect the blue wire from the thermostat to the C, but what do I do with the existing white wire that is already connected? Can both of the wires go on that terminal?

I also attached the wiring diagram for my air handler

control board picture

wiring diagram

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  1. Get a scrap bit of wire, that's the same thickness as the other wires.
  2. Disconnect the wire that is currently in the C terminal.
  3. Strip both ends of the scrap piece of wire.
  4. Connect one end of the scrap piece of wire to the C terminal.
  5. Using a twist-on wire connector (or other connector), connect the wire that was previously connected to the C terminal with the new C wire, and the other end of the scrap bit of wire.

When finished, the two C wires should be connected together, along with the wire that's connected to the C terminal.

This type of connection is known as a "pigtail".

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