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Thread: Honeywell Heat Pump - Nest said do not reconnect X wire

  1. #1
    Junior Member

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    Question Honeywell Heat Pump - Nest said do not reconnect X wire

    Hi folks

    I've been looking but I am finding it difficult to find exactly what or how I need to wire this Nest correctly.
    Firstly, I just bought this house and this is my first heat pump ever. There is no alternative heat just electric.
    I have attached the front and back of what my Honeywell Thermostat looked like and how it was wired.
    I had it connected all summer for AC ( how i thought it should be) and it worked flawlessly however when heating season showed up, it didn't work out too well.

    My concern is when I called Nest for support, they told me I did not need the wire that was connected to X on my Honeywell, connected to the Nest. Maybe I'm a skeptic but when I trace this up to the furnace it is connected to what appears to be a small transformer. I think, but not certain that it is for emergency heat. I've attached pics of my old setup and how Nest said to connect it.

    My concern....I do have heat now but I've been told that if the temps drop below 38, I should move the thermostat to EM Heat which is on my old Honeywell but I cannot find this on the Nest. Please if you have any advise, I would welcome it.

    Click image for larger version. 

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    Click image for larger version. 

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  2. #2

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    Here is a thread with some info on the X terminal

    Your white wire is for emergency/Aux heat.

  3. #3
    Senior Member

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    From your description of X going to the transformer at the equipment end it should be a common wire so connect to Nest's C. Hooking up a C wire prevents some strange problems down the road.

    Nest instructions for manually turning on emergency heat: If your system is truly all electric (no gas/propane/oil for backup) then I would move the white wire to W2/Aux which turns it on automatically. The difference is with emergency heat (*) the heat pump is not used at all. Aux runs at the same time as the heat pump so can cost more but Nest tries to minimize its use:

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