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Thread: A/C wiring

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    DIY Junior Member sandy vandehey's Avatar
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    Default A/C wiring

    Hi, We had to have our furnace temporarily moved to replace the slab in the basement, we did not do the disconnect but put the furnace back in place, everything is fine, the heat works, but we have a red and a white wire from the air conditioner and do not know what terminals to attach them to. The terminals are TWIN, Y, G, W, R, C. We matched the terminal in the thermostat to the terminals in the furnace so the heating works. The furnace is a rheem RGDG 15EARJR and is about 19 yrs old. Thanks Sandy

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    Jack of all trades DonL's Avatar
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    Quote Originally Posted by sandy vandehey View Post
    Hi, We had to have our furnace temporarily moved to replace the slab in the basement, we did not do the disconnect but put the furnace back in place, everything is fine, the heat works, but we have a red and a white wire from the air conditioner and do not know what terminals to attach them to. The terminals are TWIN, Y, G, W, R, C. We matched the terminal in the thermostat to the terminals in the furnace so the heating works. The furnace is a rheem RGDG 15EARJR and is about 19 yrs old. Thanks Sandy

    It could be for Low voltage Supply or it could be for Fan control.

    Wire color may not mean much, Or W = White and R = Red.

    More info could help.
    Theory only works perfect in a vacuum.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Take the cover off the a/c unit and see where they are attached. My guess is probably red and yellow, but there's no way to tell for sure.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member sandy vandehey's Avatar
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    I may not have been clear, the red and white wires are from the a/c unit outside and were run into the furnace control board, they are 18 or 20 guage like door bell wire, they were connected to the terminals I identified earlier, just don't know which ones to attach them to. They connect some how to the treminals with with the wires from the thermostat which controls the heat and cooling. The a/c coils in the plenum above the furnace and the unit outside were not disturbed, they were left in place, only the furnace was moved and so the wires from the thermostat were disconnected The heat is functioning fine. Hope this helps with the question. Thanks - Sandy

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    Retired Defense Industry Engineer jadnashua's Avatar
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    What you said was perfectly clear, but maybe I wasn't...it is highly likely that those wires control the a/c unit. Look at the a/c unit and see where they attach - probably the yellow and red. Then, follow them back and install them on the same terminals at the furnace. It is highly likely one is the 24vac common, and the other is the 24vac that gets turned on when the thermostat is set to a/c and it wants to turn on the a/c unit. This pulls in the power contactor and turns the a/c unit on. It should be clear if you view the wiring diagram on the furnace.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member sandy vandehey's Avatar
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    Thanks will give it a try today Sandy

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    DIY Junior Member sandy vandehey's Avatar
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    We checked the a/c unit outside and the wires connect to 2 yellow wires, white wire one wire goes to a box that the utility company installed to control run times and the red one hooks to a device that has a coil, looks something like a transformer?, so may have to call a hvac co, hate to pay a service call for someone to hook up 2 wires. Any other thoughts? Thanks - Sandy

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    Jack of all trades DonL's Avatar
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    Quote Originally Posted by sandy vandehey View Post
    We checked the a/c unit outside and the wires connect to 2 yellow wires, white wire one wire goes to a box that the utility company installed to control run times and the red one hooks to a device that has a coil, looks something like a transformer?, so may have to call a hvac co, hate to pay a service call for someone to hook up 2 wires. Any other thoughts? Thanks - Sandy
    Is there Voltage on these wires ? Around 24 Volts or so ?

    If so, Then they may be looking for a contact closure, to make the outside unit run.

    If not then it may be looking for 24 Volts, Or the utility company opens that circuit so that it stays Off.

    As Jim said "It should be clear if you view the wiring diagram on the furnace. "

    Maybe the wires are no longer used. What kind of thermostat do you have ?

    It is a guess without being there.
    Last edited by DonL; 02-19-2013 at 04:47 PM.
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    DIY Junior Member Failure2Comply's Avatar
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    One of the wires from the outdoor unit should go to "Y" and the other to "C", which is "common" on your low voltage transformer. Look a the wiring diagram in the outdoor unit and see what factory wire goes to one side of the compressor contactor "common" terminal. That one will be "C" from the furnace.

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    Jack of all trades DonL's Avatar
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    Quote Originally Posted by Failure2Comply View Post
    One of the wires from the outdoor unit should go to "Y" and the other to "C", which is "common" on your low voltage transformer. Look a the wiring diagram in the outdoor unit and see what factory wire goes to one side of the compressor contactor "common" terminal. That one will be "C" from the furnace.
    That sounds correct for the norm.

    The box that the utility company installed, may just open (in series with) the Y wire using a relay. Just a guess, That may depend on the thermostat used.
    Theory only works perfect in a vacuum.

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