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Air Compressor Problem - Motor Stalls

Discussion in 'Electronic Repair' started by Sparks Fergusson, Mar 4, 2010.

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  1. I'm having a problem with my 20 gallon, single stage electric air
    compressor. It's acting like the motor is underpowered - it pumps up
    to about 95 psi ok, but then the motor stalls. The unloader bleeds the
    pressure off, the motor restarts, runs for a couple of seconds, and
    then stops again...repeat...repeat...

    It worked fine for years (The pressure switch would shut it down at
    about 120 psi) but over the past few months, it's gotten worse and
    worse, and now will only make about 90-95 psi before the motor stalls.

    I cleaned and lubricated the compressor itself, and it spins freely
    and doesn't appear to be binding or otherwise have excessive friction.
    The check valve/unloader is working and the piping is all open and

    It seems like the electric motor (1/3 hp) just no longer has the oomph
    it used to. It starts up fine, no humming, no smoking, no bad smells,
    no clunks. It just doesn't seem to have enough running torque to
    handle the load like it did before.

    Anyone have any ideas?

  2. PeterD

    PeterD Guest

    Bad pressure switch. The unloader is part of the pressure switch so if
    it is being activated, the pressure switch is 'saying' that the
    pressure is sufficient. Maybe it is just mis-adjusted.
    Check the adjusting screws, and reset the cutoff back to 120 PSI.
    Confirm the cuton is at 95 PSI.
  3. GregS

    GregS Guest

    Check the line voltage while opperating at the motor.
    I can do that stall with a long extension cord.

  4. GregS

    GregS Guest

    Is it oiless ?If so, check the bearing.

  5. It's an AC induction motor, so no brushes. Could it be a capacitor
    It's a combination check/unloader valve. I cleaned and lubricated it,
    and it appears to be working fine. The tank holds pressure - the
    unloader just vents the tube between the tank and the compressor.
    Good thought, but the pressure switch seems to be functioning well. I
    am getting around the problem by turning down the pressure below the
    point where the motor stalls. But, that's only about 90 psi, which is
    not as much as I'd like. Plus, the problem seems to be getting worse.

  6. Actually, it's a mechanical unloader (combination check
    valve/unloader, which I have already cleaned and lubricated.) It seems
    to be working well.
    The pressure swicth seems to be working fine. If I turn down the
    pressure adjustment, I can get the contactor to turn off the motor
    before it stalls, but that's only 90-95 psi or so. If I adjust it
    higher, the motor is unable to turn the compressor if the pressure is
    more than 95-100psi. It's definitely the motor stalling, not the
    pressure switch opening.

  8. I can turn it easily by hand, so it doesn't appear to be binding.
    However, I don't have an easy way to check it when it's at full load.
    Any suggestions?

  9. Well, it's been working for a long time, but over the past few months
    has been exhibiting the stalling issue.

    I guess the guage could be wrong, but I kind of know what 120psi
    "feels like" and it's not getting up to what it used to, either by the
    guage or by feel.
  10. GregS

    GregS Guest

    The compressor speed does not slow down normally, it just starts to
    sound a bit different under load.

  11. Nameplace current rating is 6.0 amps (I'm running on 120 volts.)

    I measured about 5 amps at startup (0 psi) rising to close to 6 when
    it stalls. When it stops turning, the current actually drops back
    closer to 5 amps, then increases as the motor starts turning again.

    The motor is also hot to the touch after pumping all the way up. I can
    hold my hand on it for maybe 6 or 8 seconds. I don't know if that's
    different from how it used to be, though.

  12. It didn't used to, that's for sure. Now, it slows all the way to 0. :(
  13. Alan Douglas

    Alan Douglas Guest

    Assuming it's a 120V/240V motor connected for 120, can you check to
    see if both run windings are actually connected? Perhaps a nut is
    working loose on the terminal plate inside the motor.

  14. No load, it's drawing about 1.5 amps. It gets warm, but not as hot as
    it was under load.
  15. Hmm, you might have something, there! This motor is probably 15+ years
    old, and has never had anything done to it. Could corrosion and/or
    loose connections account for the lack of power? I can certainly try
    cleaning and tightening anything I can get to.

  16. It's some sort of GE induction motor. I have the model number, but I
    can't find anything about it on the GE website or Google.

    What sort of problems would high no-load amp draw suggest?
  17. "William R. Walsh"
    Pressure switch contacts look OK, and there's minimal voltage drop
    across under load. Wiring looks OK, too.
    There is a capacitor, but I'm not sure exactly what it does. I don't
    have a wiring diagram and can't find any info on the Manufacturer's
    website (GE.) I'll try to check the capacitor as best I can.

    Could a capacitor issue cause the motor to start fine, but not have
    enough power when running?
  18. Jamie

    Jamie Guest

    Bad bearings..
    and if it's a single phase motor.. check the starter cap, if it
    has one. most likely not much good any more..

    Also, you may have a centrifugal switch in the motor that isn't
    closing its contacts. Or, you could have an open winding!..
  19. Alan Douglas

    Alan Douglas Guest

    Assuming it's a 120V/240V motor connected for 120, can you check to
    None of the other suggestions I've read, fit the symptoms. First
    would be low voltage to the motor under load, but you've already
    checked that. The starting capacitor is out of the circuit when the
    motor is up to speed. There's nothing left in circuit but the two run
    windings, wired in parallel.

  20. PeterD

    PeterD Guest

    And all those replies ignore the fact the unloader is operating (at a
    wrong, low pressure) which certainly doesn't point an evil finger at
    the motor at all...
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