Sears compressor

both motor and switch make a humming noise but compressor will not start?
How do you check the compaciter?

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Bill says...

If the switch is humming, that means to me that the points aren't closing fully, and that's reducing the power flow to the motor, which may be why it's humming too.

I'd check out the pressure switch first.

As to testing the capacitor, take it, and the motor, to an electric motor rebuild shop and ask them to test it. The, if it's either, they can repair or replace it for you.

But I'm betting it's your pressure switch.

Cheers,

Bill