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Thread: Honeywell RTH6580WF WiFi Thermostat C-Wire Connection

  1. #1
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    Honeywell RTH6580WF WiFi Thermostat C-Wire Connection

    Purchased for A/C only. Heater is controlled by separate thermostat
    Old, mercury thermostat has only R, Y, and G wires
    Can readily drop a wire to the air handler in basement but don't know where to connect it and whether I need to run entirely new 4-wire cable or if I can run the C-Wire independently.
    Am attaching photos of:

    1. thermostat wires going into air handler and wires out to compressor. Note that cable with green wire wrapped around it goes to compressor. Other cable with multi-colored wires wrapped around are from thermostat.
    2. internal wiring of air handler including transformer


    Any tips? I'm willing to lose ability to run fan independently.
    I know to turn off power to A/C prior to doing any wiring.

    Click image for larger version. 

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    Last edited by cgiben; 07-18-2019 at 09:51 AM.

  2. #2
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    If the thermostat cable that has the white, black, blue and orange wires wrap around it is the same thermostat cable going to your cooling thermostat all you need to do is use one of the wire that is wrap around the as the common wire. Unwrap one of the wires and connect it with the wire nut that is for the white wire from the outdoor unit (this is the white wire that is with the thermostat cable that has the green wire wrap around it). At the thermostat connect the same wire that you unwrapped at the other end to C terminal.


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