As compressor begins to build pressure, the motor slows down to nothing.

I have a Sears 919.176730 3HP 20gal oil lubed compressor. The compressor will run great providing tons of air as long as the drain cock is open. AS SOON as the tank begins to build pressure, the motor slow down to nothing. No belt slippage, just the motor/compressor dies right out. Is this a pressure switch issue?

Thanks so much...Mark

__________________
Bill says...

No Mark. I don't think it's a pressure switch issue.

If our motor is slowing the compressor to a stop, then something is doing that to the motor.

It could be that the motor can't handle the back pressure from the filling tank, and that could be that there is a power supply issue, the check valve could be a problem, the motor or run capacitor may be failing... it's so hard to try and diagnose without seeing it or hearing the compressor.

If it were mine, I'd have a local electric motor rebuild shop do a load test on the motor and capacitor to rule them out as the cause.

Cheers,

Bill

Motor Size for Craftsman Air Compressor

by Paul
(Richmond, VA)

I have an older Craftsman compressor (4hp/25gal). Looking at newer models the motors are only about 1.5 hp rated (as in 1.5hp/33gal). Are these really smaller or was there some redefining of the actual horsepower done via new labeling standards? Thanks.

__________________
Bill says...

Paul, I'm not quite sure what the question is?

Tell me something. Is your older Craftsman compressor, rated at 4HP, powered by a 120 volt circuit?

What I think you may be seeing is greater honesty in horsepower ratings. It is doubtful you could power a 4 HP motor adequately with a 120 volt circuit. You would need 220.

Maybe the older compressor power ratings were over stated?

Cheers,

Bill