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    hdhoney03's Avatar
    hdhoney03 Posts: 1, Reputation: 1
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    #1

    May 12, 2011, 10:38 PM
    New Thermostat installed now outside AC unit won't shut off.
    I just removed my old mercury thermostat from our home and replaced it with a digital one. Im almost certain I got all the wires labeled correctly but I could be wrong. Any ideas here? I haven't been running air at all this year till last week. Im just worried about wearing out the outside unit or worse.
    drtom4444's Avatar
    drtom4444 Posts: 3,282, Reputation: 145
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    #2

    May 13, 2011, 10:47 PM
    You have a short between Y and R. The wires are labeled Y= yellow and controls the outside unit contactor (relay), R= red and is the power to switches in t-stat, G= green and controls inside fan relay, W=white and controls heat relay or gas valve. On heat pumps you also have O or B for the reversing valve. Also on electronic thermostats you have a common which is the opposing side of R on the transformer. Some thermostats have a RC and a RH when two transformers are used. Just jump these together when one transformer is used which is the safest way for it to be wired because when two transformers are used you have to make sure the transformers are in sync: between RC and RH should read no voltage. Let me know what you find. DrTom4444
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