Thanks for helping me here. I am adding a new wifi thermostat to my system but need to add a C wire directly to the air handler (system is a First Co air handler with hot water boiler for heat and separate condenser for A/C). I've attached a wiring diagram. Can I simply splice into the brown wire directly off the transformer without effecting anything else?

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1 Answer 1


Yes, that should work. I'd prefer to make the splice at a terminal or an existing junction, but you can splice it in the middle of the wire just as well (as long as there's enough slack in the wire).

  • Thank you. Based on the diagram, and your comment of a terminal or junction, is there another spot you'd recommend connecting the C wire?
    – Rob
    Commented Nov 6, 2014 at 22:59
  • 1
    I'd have to see how the wires are connected at each location, to determine the best place to attach a new wire.
    – Tester101
    Commented Nov 7, 2014 at 10:52

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