Older Sears compressor just hums....?

by Dave
(Tiverton, RI)

Older Sears compressor, 220v, won't start when switch on at pressure switch. Just get electric humming noise.

This happens all the time. Pressure in tank could have bled to 0 since last use. Can sometimes get it to start by pushing belt (very carefully) and trying to "catch it" by switching on at same time. with cover off pressure switch, can see sparking going on in there during these start attempts. If compressor starts, no more sparking.

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Bill says...

The power flows through the pressure switch when the cut in pressure is reached by points inside the switch closing, and allowing power flow.

If the points are burnt, corroded, or failing in some manner, they can't close properly, are trying to, and the result is a buzzing or humming sound.

I also have heard that humming sound when the motor starter is failing, and it can't get enough juice to the motor to start it up.

I'd start by replacing the pressure switch and see if that solves the problem.

Bill