Page 1 of 2 12 LastLast
Results 1 to 13 of 15

Thread: losing 24 volts

  1. #1
    heatseeker Guest
    service call states ac doing nothing, flip t-stat to fan on, nothing, check transformer shows 110 on primary side and 0 on secondary, 24 volt side, changed transformer, turn t-stat back to auto and set to call for cooling, indoor fan starts but outdoor unit never starts, somehow losing 24 volts at condensing unit, manually pushed contactor and outdoor fan started but will not start when energized by condtrols, losing low voltage somewhere, changed contactor and that didn't help.The low voltage runs under ground from inside to out, don't visually see any problems with wiring.

  2. #2
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,513
    run a new wire and dont get nuts looking for a break

  3. #3
    Join Date
    Jun 2005
    Location
    New York
    Posts
    207
    If you didnt have 24v at the contactor then changing the contactor wouldnt help. Did you jump out the cooling at the t-stat? I would check the stat first. Fuse the transformer so you dont have to change it again, could be a short etc. jump out the cond. at the A/H and see if you get 24 out side, if not, bad wire. Is there any saftey devices outside? High / low etc, breaking power to the contactor, or is it a home run to the coil? Thats really all it could be.

  4. #4
    Join Date
    Jun 2004
    Location
    Clayton,NC
    Posts
    407
    After you changed the tranformer you have 24 volts coming out of the secondary?At the condensing unit you have 0 voltage? Why change the contactor then? Where are you checking for voltage at in the condenser? It should be checked at the wires going to the unit. Not the contactor.If you have 0 voltage then the problem is in the wire. If you have voltage then something between it and the contactor is shorted. Are there any safeties in the unit? Sometimes the wires rub against the freon lines or compressor. This would short out the transformer and cause a loss of 24 volts at the contactor.

  5. #5
    Join Date
    Jun 2003
    Location
    Florida
    Posts
    9,548
    look for the classic weed-eater signs also....
    If everything was always done "by the book"....the book would never change.

  6. #6
    heatseeker Guest

    losing voltage

    stevehvac, i am checking at the low voltage side wires of the contactor coming from inside, i did get a strange reading of 15 volts when cheked the hot low voltage wire and touched one meter lead to a ground. even ran separate wire from transformer to outside unit low voltage, done this because the original wire is in conduit, in the ground, still nothing, so i know i don't have a bad wire, but i still don' have voltage to pull in outside unit

  7. #7
    heatseeker Guest

    losing voltage

    stevehvac, i am checking at the low voltage side wires of the contactor coming from inside, i did get a strange reading of 15 volts when cheked the hot low voltage wire and touched one meter lead to a ground. even ran separate wire from transformer to outside unit low voltage, done this because the original wire is in conduit, in the ground, still nothing, so i know i don't have a bad wire, but i still don' have voltage to pull in outside unit

  8. #8
    Join Date
    Jun 2005
    Location
    New York
    Posts
    207
    This maybe a dumb question. Are you using a multi tap transformer and have it wired for 110v? Do you have 24 plus VAC at the A/H after the stat calls on Y and C ?

  9. #9
    Join Date
    May 2003
    Location
    Sarasota. Fl
    Posts
    1,275
    Check the transformer for 24 volts.

    If you have it, set the stat to cooling.

    Then check between common and yellow at furnace for 24 volts during the call for cooling.

    If you have it go outside and check it at the condenser. (24 volts)

    If its not at the condenser but you have it at the Furnace you are losing it somewhere in between.

    If thats the case, try to use some other colors of the stat wire like black and green.

    Anything that isnt being used.

    Good luck.



    [Edited by miami mike on 06-22-2005 at 10:14 PM]
    It is the job of thinking people not to be on the side of the executioners.

    ~Albert Camus

  10. #10
    hi can sombody explain the 20 split

  11. #11
    Join Date
    Nov 2008
    Posts
    1,673
    Quote Originally Posted by heatseeker View Post
    transformer shows 110 on primary side and 0 on secondary, 24 volt side
    Open winding or a short downstream? Checking the current flow in either winding will tell.
    Voltage is only half the story.

  12. #12
    Check pressure switches.

  13. #13
    Join Date
    Jun 2007
    Location
    Round Rock
    Posts
    3,561
    Get somebody out who knows what they're doing. This is really a very simple problem to fix. You might screw something up worse if you're not careful.
    I like DIY'ers. They pay better to fix.

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event