My air compressor won't build up sufficient pressure.

by Dana
(Ithaca, NY)

My compressor is a 1.5hp 175psi twin-cyl model, 230v single phase motor. It builds up about 45psi, and the motor slows down. The start capacitor switch closes and the motor speed increases enough to open the start capacitor switch, and it slows back down again.


I don't know if the fault is in the compressor or the motor. The motor seems to reach full speed and run fine with the belt off, and the compressor pulley doesn't seem to be difficult to turn. The compressor has oil, and nothing gets hot, although I don't let it run more thn 3 or 4 cycles of the start capacitor switch closing.

I don't think the motor is starved for electrical power, because the 6-20R receptacle powers my bandsaw just fine. I have not done any motor current draw tests, but the 30A breaker does not trip.

Should I suspect a faulty run capacitor? An open winding? Really bad luck?
Thanks for any suggestions, Dana.

_____________________________

Bill says...

Dana, your electrical knowledge is clearly far in excess of mine. I'm a compressed air guy, and dabble in electrical components as a last resort.

One thing I wonder about, have you checked or cleaned the check valve into the tank? If debris build up is impeding its opening as the tank pressure builds, the increased back load may account for the compressor head / motor slowing.

If you've already checked that, then you need an electrical expert to have a look.

Cheers,

Bill