Air Compressor motor slows down / stops


Old 07-28-10, 03:13 PM
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Air Compressor motor slows down / stops

I have an older air compressor. It has twin compressors that are belt driven by a 1hp 110 volt electric motor. Sometimes the motors RPM will drop drastically or stop all together. When it stops, the motor will whine and rotate occasionally. It seems to happen regardless of what the pressure in the tank is. If I remove the drive belt, the motor will spin just fine. The motor has a capacitor mounted on the side of it. Could the motor be going bad, or is the capacitor bad? Any ideas would be greatly appreciated. Thanks.
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Old 07-28-10, 03:38 PM
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Welcome to the forums! I wouldn't think it is your motor nor the capacitor, since it runs fine without a load. You may have a faulty unloader on the compressor, or you could be low on fluid. I would look to the compressor as the culprit, as it seems to be loading up too much.
Old 07-28-10, 04:28 PM
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The motor sounds okay to me. It could be the compressor seizing up from lack of oil if it is supposed to be oiled or from a malfunctioning unloader valve that is not releasing head pressure on the piston.

When the pressure switch cycles off you should hear a "PSSST" sounds as the unloader opens. If you do not hear that, then it is not opening correctly and leaving the piston under pressure. It will be almost impossible for the motor to start on the next cycle leading to the stalling symptoms you have.
Old 07-28-10, 07:18 PM
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Thanks for the info. I will check that to see if it works. Thanks again.
Old 07-28-10, 08:47 PM
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Make sure you use proper compressor oil if none avabile the standard engine oil will work but get in straight weight verison like 20 W oil or simuair like that.

Second thing is when you leave the belt off from the motor turn the compressor itself to see if you feel any binding or hard rubbing if that the case sound like crankshaft bearing going bad.

Are you refering to twin cylinder or twin compressors like two compessors to one electric motor ??


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