Trips breaker, motor hums on restart but won't turn.

by Karl
(Bristol, NH, USA)

MAC2000 portable air compressor

MAC2000 portable air compressor

MAC2000 portable air compressor (given to me by a contractor friend.) Not sure of the age (it's kind of beat-looking, but things age quickly on construction sites,) but it's probably about 10-ish years old.


Generally runs fine, but sometimes I'll be using some tool or blowgun and the air will just slowly start dropping off.

Upon checking compressor, I find the breaker tripped. Turn breaker back on, and compressor motor just hums and the compressor itself won't turn. If allowed to continue, the breaker will trip again.

Motor is not unusually hot when this happens.

After several tries to re-start it (compressor switch on-off-on-off-on-off-on) it will suddenly start running again.

Voltage supply is good at 120 volts. No extension cord is being used. Pressure is set for about 90 psi. Not running it for extended periods of time.

Does this sound like a motor/electrical problem, or is it a compressor/mechanical problem?

How do I tell which one is going on?

Comments for Trips breaker, motor hums on restart but won't turn.

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Feb 11, 2019
Humms...
by: Doug in s.d.ca.

Could be a couple or three things.

Is it leaking air when it won't start? Then try cleaning or replacing the check valve.

If not that, then check the capacitors - probably the start cap is dead or dying. OR, if it's OK, then the contact on the back of the motor may be dirty/pitted/ or otherwise broken.

Good luck.

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