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    Furnace Wiring - Adding a common "C" wire

    Asked Sep 19, 2008, 04:17 PM 19 Answers
    My new thermostat has uses a W,R,Y,G and now a "C". My wiring has only W,R,Y, and G and these are needed.
    How do I, or can I add the needed "C" wire? Is it just adding a wire from the transformer?

    Last edited by Bocaheat; Sep 19, 2008 at 04:26 PM.
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    EPMiller's Avatar
    EPMiller Posts: 624, Reputation: 37
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    #11

    Sep 30, 2008, 04:53 PM
    Quote Originally Posted by KeepItSimpleStupid View Post
    Let's make this simple. G,R,Y,G and C

    <snip>
    When R connects to Y, the furnace turns on: The furnace controls the fan (On and Off)

    When R connects to W, the outside AC unit comes on.
    <snip>
    Uhh... KISS, I think you got it backwards. Unless they do it differently in your part of the world.

    R to Y calls the compressor, which usually is cooling. If it is a heat pump then the O or B terminal (the type of reversing valve determines which must be used) decides whether it will heat or cool.

    R to W calls heat. If it is a heat pump W often is the second stage (W2) or backup heat.

    Some systems control the fan from the control board and some from the thermostat. You program your tstat accordingly if it allows you to. Otherwise R to G will call the fan (you had that correct), and the temp limiters will overide the fan call and keep it running until the system is below the limit switch threshold.
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    Bocaheat's Avatar
    Bocaheat Posts: 9, Reputation: 1
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    #12

    Oct 3, 2008, 02:19 PM
    Ok, here is what I have found. Please see attachment. When I connect the Yellow wire to "C" the fan inside turns on and stays on. (Thermostat - Furnace) RH-R, G-G, W-W1, Y-Blue wire, and finally C-B.
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    Bocaheat's Avatar
    Bocaheat Posts: 9, Reputation: 1
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    #13

    Oct 3, 2008, 02:24 PM
    Sorry, not correct! The "O" and "B" terminal on the Furance are reversed.Name:  Furnace.GIF
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    KISS's Avatar
    KISS Posts: 12,505, Reputation: 838
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    #14

    Oct 3, 2008, 02:33 PM

    Since the new tstat has Rh, there musct also be an Rc. Rc and Rh MUST be jumpered together.
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    Bocaheat's Avatar
    Bocaheat Posts: 9, Reputation: 1
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    #15

    Oct 4, 2008, 03:41 AM

    The instrucion had me insert a jumper for my configuration. I assume that was what it was for.
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    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 434
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    #16

    Oct 4, 2008, 03:59 AM


    Unless it was missed can you post the brand and model of your new thermostat?
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    Bocaheat's Avatar
    Bocaheat Posts: 9, Reputation: 1
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    #17

    Oct 4, 2008, 10:51 AM

    Ritetemp 6080
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    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 434
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    #18

    Oct 4, 2008, 10:56 AM


    If you follow this all should work. Now if the wiring color has not been followed by the original installer then you might have to track down the wiring and start over.

    The RiteTemp Support Site - 6080 Technical Support Page
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    Bocaheat's Avatar
    Bocaheat Posts: 9, Reputation: 1
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    #19

    Oct 4, 2008, 11:00 AM
    I rechecked the wiring and it seem to be working now. Thanks.
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    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 434
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    #20

    Oct 4, 2008, 11:07 AM


    Glad you got it going. Keep the web site for future use if necessary.
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