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O/T Air compressor motor problem

A

Anonymous-0

Well-known Member
Porter Cable air compressor with an A.O Smith single phase AC motor. Hums and trips breaker when turned to on position. Took front cover off to inspect piston and it is good and moves freely. I can spin the motor freely by hand so there is no binding. What is the best way to go about troubleshooting this motor. My first thought is that the starting coil may be bad. But I cannot get it to start when I turn it by hand and flip the switch to on.

Any thoughts?

Thanks,
-steve
 
Sound like you are on the right track and you have a bad starting capacitor. That would be the most likely thing that I have seen in my limited experience.

I would think it would start if you roll it over by hand like you tried but maybe you are not able to spinning it fast enough for it to really start.
 
My first thoughts were the same. Beyond that, the running cap may also be bad, or an open circuit somewhere. You"re at the point whee I take them to a motor shop.
 
Had same problem with different.....but similar.....brand. Contact points in switch box were burned. Filed/scraped them clean and it went back to working..........
 
If the starter switch and start capacitor are good. Is there an un-loader that supposed to "de-stroke" the compressor until it's up to speed?
 
Not familliar with your motor, but many use a centrifugal switch to toggle between the start and run sides of the capacitor. The switch puts the start capacitor in the circuit until the motor reaches the run speed, then switches to the run side. Your switch could have burned contacts, making poor, or no contact at all. It could also have a broken spring/s causing it to be inoperable. Inspect the switch if one is present, and if it looks OK, check both sides of the capicator with an Ohm meter. You should see the needle kick when the leads are placed actoss the terminals if it's OK. No kick most likely = bad capacitor.
 
Dave,

Turned out to be the centrifugal switch like you mentioned stuck. I took my cordless drill and spun the motor to free it up. Motor is running like a champ again.

Thanks for everyone's help,
-steve
 
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