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  1. #1
    Join Date
    Mar 2012
    Location
    Hattiesburg, MS
    Posts
    16

    Air handler not coming on with condenser

    --------------------------------------------------------------------------------

    Hello, new to the site, would appreciate any help. My A/C was running and then the air handler shut off but the condenser continued to run. The house was not cool (not a stuck contactor) and now the air handler wont come on (It will come on in heat mode, just not in cool). I am getting voltage on both sides of both transformers (its a gas furnace) and the only way to turn on the air handler is the switch on the handler. It is an older unit (no board), and the switch has 3 positions (ON, OFF, FAN). It would normally be in the ON position, but currently the only way the handler will turn on is in the FAN position. I am steadily checking different parts, t-stat is next, but if anyone can point me in the right direction that would be sweet. The unit is a Nordyne model # MGHA-075ABFC-01. I am a universally ceritfied tech thru Esco, but still relatively new to HVAC. This is teh A/C at my house.

  2. #2
    Join Date
    Sep 2008
    Location
    VA
    Posts
    1,717
    Sounds like you fried your new stat with 48-54 volts. Time to Call a pro.
    "The only true wisdom is in knowing you know nothing" Socrates

  3. #3
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,619
    isn't this a duplicate thread ?
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  4. #4
    Join Date
    Sep 2008
    Location
    VA
    Posts
    1,717
    Sorry my friend, but this is sounding like we're doing a side job for you. You can probably imagine how much a professional tradesman enjoys giving work away to non professionals.
    However, if you are certified as you say, then I would suggest building your post count and applying for pro application on this site. There are loads of skilled technicians in the pro section that will help you diagnose just about anything.
    Sorry, I don't mean to be rude, but our trade is polluted with guys who think they can buy a meter and gauges, go out and charge people for a job they're not qualified to perform, thus further enforcing a stigma us professionals try so hard to refute.
    "The only true wisdom is in knowing you know nothing" Socrates

  5. #5
    Join Date
    Mar 2012
    Location
    Hattiesburg, MS
    Posts
    16
    No, not a side job. Not a new t-stat either. Any sidework I do is with my tech school teacher or with someone else who knows far more than me. I am not comfortable working on too many people's equipment by myself. Also, the trade may be polluted with pretenders, but those guys make a bad name for themselves and when tehy screw up big, someone competent gets called. Definently would not consider myself a "pro", and too much posting would further reveal my ignorance. Yes it is a repost. Initially i posted and was asked for credentials, i then provided and was then told that I might have more replies reposting in Tech 2 Tech chat room. So, there is that. This is truly my unit i am asking about, luckily it is nice enough weather that open windows will suffice until I can fix this baby. For anyone who cares to bring the claws in, the unit was running when the air handler kicked off. The condenser continued to run. Now, when i try to turn on the A/C, the condenser kicks on, but no air handler. The handler will come on if i turn on in heat mode. Any takers? Thanks.

  6. #6
    Join Date
    Mar 2012
    Location
    Hattiesburg, MS
    Posts
    16
    Just took the TSTAT off and wired together, voltage, common, and cool wires; condenser came on, still nothing from the air handler.

  7. #7
    Join Date
    Dec 2004
    Location
    Chicago area
    Posts
    1,438

    Fan relay.

    "Just took the TSTAT off and wired together, voltage, common, and cool wires; condenser came on, still nothing from the air handler."

    What do you mean voltage common and cool wires?

    Sounds like a fan relay in the furnace.

  8. #8
    Join Date
    Mar 2012
    Location
    Hattiesburg, MS
    Posts
    16
    RC-voltage
    Y-cool
    G-common
    These are the terms I know, but basically, I twisted the wires together that should turn on the A/C. My thinking was that maybe the TSAT (its an old one) wasnt sending right signal, so why not bypass it. I ohmed out the relay, but the diagram I have doesnt show whether or not the positions are the relay are suppossed to be normally open or closed. Maybe Ill try a new relay and see if that fixes the problem, but nothing open today, so any other feedback would be sweet. Thanks.

  9. #9
    Join Date
    Oct 2005
    Location
    Pacific Northwest
    Posts
    2,261
    Quote Originally Posted by bigfleen View Post
    Just took the TSTAT off and wired together, voltage, common, and cool wires; condenser came on, still nothing from the air handler.
    Let go, step back and get help, ok? You really do need a pro.

    I suggest hounding the Sh*t out of him when he gets there. They love that.

  10. #10
    Join Date
    Mar 2012
    Location
    Hattiesburg, MS
    Posts
    16
    Advice like, call a pro, hound him when he gets there, super helpful. So if your mower breaks down and you dont know exactly what the problem is right away, do you call someone to fix it? Prob not, you tinker, and guess, etc. Are you dealing with high voltage on your mower, no, but blades spinning at high rpm can be pretty dangerous. I understand everyone's unwillingness to give valuable advice away, but really, if a DIY gets on here and scews up, he is going to have to call a tech in the end anyway. Whats the point of a site with Tech 2 Tech and AOP if the answer is always call someone?

  11. #11
    Join Date
    Apr 2006
    Location
    Barrie Ontario
    Posts
    312
    Just curious as to why you're so convinced its a 24v problem
    For some reason I learn more with my mouth shut

  12. #12
    Join Date
    Mar 2012
    Location
    Hattiesburg, MS
    Posts
    16
    Im not. 1st post said that the TSTAT was fried.

  13. #13
    Join Date
    Mar 2012
    Location
    Hattiesburg, MS
    Posts
    16
    Whatever the problem, it is limited to cool mode. I am still learning, so I have been checking everything that I can think to check. i was hoping it was going to be someone easy to figure out like a transformer or tripped breaker (lol). No biggie though, i can definently use the practice trouble shooting.

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