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  1. #1

    No Power to A/C Thermostat

    Hello All, I'm new here and have a question that I hope someone can help me with.

    My A/C thermostat started acting weird a few days back. I have a simple digital stat, with a greenish-glow backlit screen, with settings for cool, heat, and fan. All of a sudden, the screen went blank, no light, and the A/C of course would not kick in. Initially I thought the stat must have gone bad, and I was gonna get a new replacement. Decided to take it off the wall mount and check it out. Removed the green and red wires and put them together, the fan didn't kick on...no power? Tested it with a multi-meter, no power at all from any of the wires. So...it's not gonna be a simple stat replacement afterall.

    The strange thing is, after messing with the wires on the stat, and turning the main A/C breaker on and off, suddenly the stat came back to life. Lighted up and settings displayed, A/C kicked in, and this lasted for a couple hours, before it went dead again. That was late last night. Early this morning, my wife said she saw the stat working. Late morning when I woke up, it was dead again.

    From my recent research on this forum, as well as eleswhere on the internet, I suspect it could possibly be the transformer. But I have no idea where that is! Just to make one thing clear, I am not savvy with electrical stuff, I'm pretty handy mechanically, and can follow instructions well though. So, I opened up the air handler in the garage, looked inside at the bunch of wires, there were some similar thin wires as the wall mounted stat's. I tested those with the multi-meter and got positive readings around 18 V.

    Now I'm thinking it must be somewhere else...so I opened up the panel in the condenser(?) at the back of the house (the noisy one with the fins and fan). Tested the terminals where the power enters (A & B) and is connected to some device (attached pic below) and got around 110-120V. Tested the other terminals (C & D) which look like where the power gets distributed to those familiar thin wires that I saw on the wall stat. No Power there...so I assume I've found the culprit!? Well, being an amateur, I am not sure. And that's why I'm here. Oh, btw, there's no power at the terminals of those thin wires (bottom right corner of the first pic below)that look similar to (or leading to/from) the thermostat's inside the house.

    Here are some pics of the panel in the condenser/compressor (sorry, I don't know the correct name for this noisy thing! LOL!). Can someone confirm if this is the transformer, if not, what is it called? There looks like a little contact point, I guess for the timer to kick the thing on/off. Judging from my description, is this the faulty part, and should I attempt to replace it myself since I have come this far?

    I am one of the many unfortunate unemployed ones, and would rather do this myself, if I can. If I have to, I don't mind getting someone to do the job, if there are big risks involved.

    Thank you all.












  2. #2
    Join Date
    Dec 2008
    Location
    Buffalo NY
    Posts
    3,140

    Cool

    This is high voltage and you really could hurt yourself if you do not know what you are doing. You should really call a pro. Tell them your plight and they may help you out.
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  3. #3
    Join Date
    Jun 2008
    Location
    Rochester, NY
    Posts
    61
    You need to call in a professional to diagnose and repair the problem. This is not a DIY site.

  4. #4
    Join Date
    Jun 2007
    Location
    Round Rock
    Posts
    3,617
    Nobody is gonna help you here. You could kill yourself and nobody wants to be responsible for that. Your wife might sue somebody. It was a pretty good presentation though. Check your breakers, aside from that. Find somebody to call out and they'll take care of you. Probably nothing too difficult. They'll let you know when they get there.
    I like DIY'ers. They pay better to fix.

  5. #5
    Join Date
    Jun 2008
    Location
    NW Florida
    Posts
    709

    Wink

    Quote Originally Posted by bmathews View Post
    Nobody is gonna help you here. You could kill yourself and nobody wants to be responsible for that. Your wife might sue somebody. It was a pretty good presentation though. Check your breakers, aside from that. Find somebody to call out and they'll take care of you. Probably nothing too difficult. They'll let you know when they get there.
    That part is the contactor. I do not believe that is your problem. It is very dangerouse for an experienced tech to check this out. Much less an inexperienced home owner. Call a PRO. Before your wife has to call an ambulance.

  6. #6
    Join Date
    Oct 2008
    Location
    Indiana
    Posts
    78
    Cosmos,
    As has been mentioned, this isn't a do-it-yourself site. Honestly, you should call in someone to troubleshoot this for you. It does not sound like anything that will be complicated or expensive to repair.

    And please stay out of the outside unit. There's 240 volts in there and it's *not* the source of your problem!

  7. #7
    Wow...this is pretty intimidating!

    But I do understand all your concerns, Thank you All for your responses anyway. I will stay out of the condenser unit now.

    Do you all think the problem is with the thermostat, dirty contacts, etc... I don't think so coz' there is no power on those 24V wires from the wall.

    Also, the stat just came back to life just now, and the AC is running, but I don't think for long. It cuts on and off at random, what could be causing it?

  8. #8
    Join Date
    Oct 2008
    Location
    Indiana
    Posts
    78
    Quote Originally Posted by Cosmos View Post
    Wow...this is pretty intimidating!

    But I do understand all your concerns, Thank you All for your responses anyway. I will stay out of the condenser unit now.

    Do you all think the problem is with the thermostat, dirty contacts, etc... I don't think so coz' there is no power on those 24V wires from the wall.

    Also, the stat just came back to life just now, and the AC is running, but I don't think for long. It cuts on and off at random, what could be causing it?
    The thing is, this site is very particular about not providing info for do-it-yourselfers to troubleshoot their own systems. If you search a bit you can probably find a site that caters more to DIY repairs.

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,564
    It may have started working again.
    But its only a matter of time before it stops again.

    Call a contractor.

    Thread closed
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