Need help w/ air compressor problem

[Steve Carbone]

I'm having a problem with my CH 4 gallon oilfree air compressor. It's about 4 years but has seen very little use. When I turn it on, the motor starts up just fine. It runs for about 10 seconds but when the pressure gauge reaches about 20-25 psi the motor starts to slow down, then stops completely, hums for a few seconds then trips the breaker. It's plugged into a dedicated 20 amp outlet (I tried it on other outlets with the same results). I cleaned the check valve but that didn't help. Any suggestions as to what the problem could be? Thanks.

[Bond Turner]

Sounds like the motor is grounding when under a load or the compressor is sezing after some operation when heat starts to build. Unfortunately the repair probably costs as much as a new one give or take, but it might be worth running over to a local service center for your particular compressor. Good luck.

[Tom Veatch]

... Any suggestions as to what the problem could be?

Shooting in the dark, blindfolded, but it sounds like a capacitor problem to me. My compressor motor, like many, is a "capacitor start, capacitor run" motor, and perhaps your's is also. If so, it will have two capacitors, a start and a run capacitor. A short description of various motor types can be found here (http://www.iprocessmart.com/leeson/leeson_singlephase_article.htm). The cap start, cap run type is described near the bottom of the page.

It sounds like your motor is developing plenty of torque to start, but as the tank pressure increases, so does the torque requirement on the motor. Your motor comes up short of the required torque at about 25psi tank pressure. If your motor has two capacitors, the one with the lower MFD rating (should be marked on the capacitor case) is the run capacitor. A visual check may show that it's damaged, leaking, etc. Even if there's no visual evidence, they are fairly inexpensive and it would be worth the gamble to replace the capacitor to see if that fixes the problem.

Another type of motor that uses a run capacitor is the Permanent Split Capacitor (PSC) type. It will only have a single capacitor but due to the starting torque requirements of an air compressor, I doubt that would be the type of motor you have. But it's still possible that if your motor only has one capacitor, it could be a PSC with a bad run capacitor.

I'd check it out before you do anything that's very expensive.

[Steve Carbone]

My motor does have two capacitors. I'll try replacing the run capacitor and see what happens. It's certainly worth a shot. Thanks.

[Alan Schaffter]

Remove the belt, turn on the motor, and see how it reacts.

If the run capacitor is bad it will likely do what it has been doing. It can also be a problem with the centrifugal switch inside the end housing on the motor not disengaging the start capacitor- the contacts could be fuzed keeping the start capacitor engaged all the time.

Is the compressor hard to turn by hand before you start? Or after the motor trips the breaker? That might mean heating and siezing in the compressor bearings or cylinder, though if it only takes 10 seconds to kick off I don't think so unless the compressor is hard to turn from the get go.

Are you trying to run a motor wired for 220V on 110V?

Or it could be one of the suggestions previously posted.

[Don Eddard]

Remove the belt, turn on the motor, and see how it reacts.

This is a 4 gallon oil-free compressor. Chances are there's no belt.