compressor will not stop running

by Bob
(Goldsboro NC USA)

Craftsman air compressor, 20 years old will not stop running unless pressure switch on/off lever is moved to off position even after safety relief valve has blown. Manual says high pressure cutoff is about 100 psi but it runs past 120psi. Contacts appear to be in good shape and work fine with manual switch. Can get new pressure switch from Sears for about $54.00 but would like to know other things to check before replacing the whole switch

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Bill says...

Howdy Bob:

As far as I'm concerned, the symptoms you describe are those of a failed pressure switch.

The pressure switch works on a diaphragm of sorts, and as the pressure builds, the diaphragm reacts to that pressure, ultimately tripping the points open so the motor stops.

Your Pressure Switch problem may not be points related, as what I'm thinking.

I think you need to replace the switch.

Cheers,

Bill