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  1. #1
    Join Date
    Jul 2009
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    New thermostat now AC wont come on

    History is this stupid me...
    I had a failing condenser fan (squealing like a mad woman) about 5 months ago so I got new one and replaced it. The model I got from Grainger was one that can be reversed simply by unplugging two wires and swapping them. (CW = purple to purple yellow to yellow CCW = purple to yellow purple to yellow) so I didn’t secure this pigtail well and eventually after 5 months it vibrated loose and got chopped in fan. Simple splice with new connectors and all seemed fine. EXCEPT… All seemed to work correctly after putting back together but runs all the time for hours. Even more interesting is that it only does this if the thermostat is set to anything below about 80 degrees. If you walk over to the stat and dial up to 85 everything shuts off like expected. So I let this go for 2 days but electric bill will be outrageous so I did some reading and thermostats are cheap and went to home depot bought a Honeywell RTH3100C took old Trane Baystat 239 with aux heat off, followed the instructions and proceeded to install. Was easy enough till got to the “T” brown wire but found out not needed on this digital one so left it disconnected. Flipped all the breakers back on switched new thermostat to cool and set to auto heard a few clicking noises from outside unit and the inside air handler( I can’t remember if the air handler actually came on or just clicked too). So shut all breakers off again back on and still nothing not even if you turn stat to “on”
    Any help would be appreciated. Would like to limp along for rest of summer unit is on 17th year so the days are probably numbered Just don’t have the cash to shell out several grand right now for new one.


    NEW: The instructions said if both O and B then connect B to C so I did. Should I move B to B ?

  2. #2
    Join Date
    Dec 2006
    Middle Tennessee
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    a t-stat can be wired incorrectly 100 different ways

    there is only 1 correct way

    some stats use different letters to control different componenets

    this is why a pro should be called to work on your system

    oh and, your camera is out of focus


  3. #3
    Join Date
    Jan 2004
    Post Likes
    Sorry, this is not a DIY site. So we are not allowed to give out DIY advise.

    Please read Site Rules Thank you.

    Thread closed.
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