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Ecobee 3 Installation...Extra C Wire

chad.jochad.jo Chicago, ILMember

I need some advice for my Ecobee 3 installation. There’s no C wire at the thermostat; so I know I have to use the Power Extender Kit. But back at my HVAC control board, there’s already a C wire that runs somewhere else. (I can’t see where it goes…maybe to my humidifier?) My plan is to remove that C wire (and the other four wires) from my HVAC control board, and connect all five wires from the PEK to my HVAC control board according to the standard directions. Can I also the connect the original C wire to the PEK to make sure there’s still power supplied to whatever it’s supplied to now? In other words, can I have two C wires connected to the C terminal on the PEK…one for the kit to supply power to the Ecobee, and the other to go wherever it goes now? Thanks!



  • kevinmcckevinmcc Macomb, ILMember
    edited July 29

    The C wire you see is likely running to your outdoor AC unit. You don't want to disconnect that. You may also have an extra wire on Y for the outdoor AC unit, you don't want to disconnect that either. Typically they are colored red and white.

    You want to only disconnect the wires that go to the thermostat, leave the other wires in place. Connect PEK to the air handler terminals, and the thermostat wires to the PEK.

  • chad.jochad.jo Chicago, ILMember

    Thanks for your response. I was able to figure it out (eventually). The C wire went to a solenoid on my humidifier. Since I only needed one wire (that used to go to my humidistat) to go to the ACC+ port on my Ecobee, I was able to re-purpose the other wire to my humidistat, splice it to the C-wire, and send that to the C port on my Ecobee.

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