Air compressor motor problem

[84scrambler]

I have a campbell hausfeld 60 gallon compressor I picked up that is having problems with the motor starting. Its a 220 single phase motor with a start and run capacitor. I don't know to much history on the motor as I bought it used with this problem. I currently have it off the compressor and am bench testing it. I am currently testing it with just the two legs of the 120V wired up and no ground. When I plug it in the motor hums very loudly and turns over very slowly. If I let it do this for about 30 seconds the thermal overload switch gets tripped and I have to wait for it to cool down. During this slow turning I can give it a helping hand and twist the shaft and get the motor to spin up and it runs with no problem. This led me to believe the start capacitor is bad so I bought a replacement, installed it and experienced the exact same problem. Could there be any other issues causing my problem or is there some chance I got a broken start capacitor (start capacitor I am using is roughly 160-190 MFD)?
I did try a third start capacitor with a slighty different MFD (I believe it was 150-180MFD) rating from another motor that works and still had the same problem. Thanks for any input.

 

[Mellotron]

Sounds like the starter field coil is dead. Run a continuity check on it and see if you get a reading. My father had also had problems once with the centrifugal switch getting stuck and killing capacitors. Doesn't sound like you have that problem though. The end result is usually an exploded cap. Thats all I got. The pro's here will chime in soon.

 

[84scrambler]

Any idea what kind of resistance I should be seeing if I measure it? Is the starter field coil something worth replacing or ordering for that matter or is the motor considered dead? Thanks

 

[Mellotron]

Resistance would depend on the motor and it's specs. However, what's more important is that you have some resistance/continuity and not Zero. Usually a professional shop has to be used to rewind and rebuild the motor. Replacing might be cheaper.

 

[OccupantRJ]

Sounds like the Centrifugal switch is not making contact during the start mode. I have found pieces of winding lashing thread trapped between the contacts. Your ability to "kickstart" the motor points towards this.

RJ