When building pressure, the compressor slows and then stalls with a hum.

by Jay
(Playa Del Rey, CA)

I have an Hitachi EC-12 system. I have had this problem before. When I first pressurize it seems to build to 120 on the tank, and stays regulated to around 90psi where I set it. When trying to build pressure the compressor sounds like it is slowing down and then seizes with a hum. If I try to restart, the hum is heard and no compressor is running (stalled). If I let the air bleed down completely, it will start up, but slow and stall again at a much lower pressure than before. Checked the oil level,..full. Removed all lines attached to reduce any potential load. No change.
Is this a part problem where I can replace it myself, and why does this happen?

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Bill says...

Jay, that you removed the lines to eliminate load and the problem still occurs suggests to me that you are experiencing motor failure.

If it were me, I'd remove the motor, take it to an electrical motor rebuild shop, and have them test it.

The motor lugs because it cannot handle the increasing load of normal compressor use. It sounds like yours sometimes cannot even handle the load of it running unencumbered.

Check the check valve into the tank too, will you?

Cheers,

Bill