Air Compressor Question

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Old 01-22-14, 10:30 PM
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Air Compressor Question

I read through most the compressor threads and didn't find one that matched my question, so I will ask here.

The compressor is a small Craftsman 125 max psi oiler. (model 921.153101) I only use it with my brad nailer. It was running along fine then stopped and started making a humming sound. I noticed the lights dim as well.

I did some preliminary checking and the pressure switch looks good. I pulled the shroud looking for signs of overheating or shorts and didn't find anything. Oil level was good as well.

I suppose it could be the run capacitor? Any ideas would be greatly appreciated!

Thank you!
 
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Old 01-23-14, 05:26 AM
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I would first unplug the unit and see if you can turn the motor & compressor by hand. If it does not turn it's possible the motor or compressor have seized. If it turns then I would check the capacitor.
 
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Old 01-23-14, 05:46 AM
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Sounds like an electrical problem. Have you checked the capacitor? If not the cap, maybe the centrifugal switch inside the motor is stuck in contact with the starting windings.

Ps
Just did a quick search for parts on your unit. I don't get it, the 2 capacitors cost more than the piston kit Definitely check before replacing.
 
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Old 01-23-14, 06:08 AM
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If you are running it on an extension cord, try removing that, and plugging it directly into a receptacle.

You said that it was running fine and then stopped. Did you mean that it stopped before reaching full pressure, or did it reach full pressure, stop, and then would not restart? If the latter, I would drain the tank pressure down to zero and try starting it. Could be indicative of a valve or unloader problem.
 
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Old 01-23-14, 11:00 PM
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So after reading your posts I pulled the fan blade assembly off and checked the centrifugal switch. It is fine. However, I removed the switch and tried to turn the motor shaft - no luck. So it would seem the motor is seized.

I'll check the price tag for a new motor, but I'm thinking it might be better to toss this one and get a new compressor. This one is around 10 years old and it's probably time to retire it. Thinking back on it I believe I only paided about $90 bucks for it. At 10 years of service, that's less than $10 bucks a year.

Not bad for a cheap little Craftsman. )

Thank you all very much for your great help!
 
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Old 01-24-14, 05:34 AM
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If the compressor is toast it's time to bring out the WD-40 or other oil. See if you can lubricate the bearings at either end of the motor. Devices that sit long periods without being used can rust & stick in place. A little oil and appropriate force to get the armature turning could buy you several more years use.
 
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Old 01-25-14, 07:55 PM
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Ok. I'll give it a try! Thank you!
 
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Old 01-26-14, 06:28 PM
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UPDATE: ok, so I followed Pilot Dane's advice and did a little more work on the compressor. I pulled the cylinder head, drained the oil, etc. I lubbed the front bearing and cleaned everything thoroughly. Re-oiled the cylinder, piston, rings, etc., added fresh compressor oil and put it all back together.

When I plugged it in and switched it into auto mode it fired right up and filled the air tank perfectly.

I really appreciate everyone's help, and Pilot Dane's advice. Apparently it just needed a little attention. Saved me $$$.

Thank you!
 
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Old 01-27-14, 04:00 AM
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IMO most people today are too quick to throw something away instead of seeing if it can be repaired.
Glad you got it fixed
 
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