compressor starts but humms

by Big Scott
(NJ)

When I plug in my compressor sometimes it starts other times it makes a humming noise and then the circuit breaker goes.

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Bill says...

Next time you get your compressor running, let it pressure up to cut out pressure, and listen near the pressure switch to hear if it unloads. If it does not, it could be a periodically malfunctioning unloader valve.

If the unloader works each time, then I'm guessing it's your starter capacitor or motor itself.

Cheers,

Bill