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Thread: drawing 9 volts

  1. #1
    Join Date
    May 2007
    Location
    california
    Posts
    223

    drawing 9 volts

    I walked up to Carrier rtu today that was suspected of not having power. when I pushed the contacter in the compressor would start. When i tried jumping r-w or r-g or r-y Nothing would activate. I checked voltage and was drawing 9 volts from r to ground. what would cause this voltage reading? bad transformer.?

  2. #2
    Join Date
    Jan 2010
    Posts
    6,380
    Did you check the secondary voltage at the transformer with load then no load ?

  3. #3
    Join Date
    May 2009
    Location
    Waterloo Ontario
    Posts
    58
    What he said. This is basic troubleshooting, start at the source, and trace until you find where your loosing Vac.

  4. #4
    Join Date
    Dec 2012
    Posts
    6
    Check ur transformer if it's good then check ur low voltage wiring even wire nut nuts and plugs.

  5. #5
    Join Date
    Jun 2012
    Location
    East tx
    Posts
    164
    Check your supply voltage to your primary side of transformer, make sure correct voltage is being used.
    Then i would check on output side of transformer,
    If all good there check for loose connections, and possible bad coils.

  6. #6
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,373
    Bad splices/connections can be gremlins in a machine. Look for connections that are twisted and taped instead of having wire nuts on them. I've seen a few bad ones.

  7. #7
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,635
    "pushing" the contactor in will bite you inn the ass one of these days

    if you never see a part start compressor winding, you'll be fine
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  8. #8
    Join Date
    Mar 2009
    Location
    Mid-Mo
    Posts
    3,596
    Quote Originally Posted by dandyme View Post
    "pushing" the contactor in will bite you inn the ass one of these days

    if you never see a part start compressor winding, you'll be fine
    Or a compressor shorted to ground....

  9. #9
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    18,809
    In a carrier RTU, if I have low voltage, the very first place I go is that high temp cut out with the little red button over in the blower section. Then I look to see if there's a smoke detector wired in.

    After that, I look at the transformer as explained above.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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