When I turn on the compressor, it hums, but the pump doesn't start up. After a short while, the overload button pops. I reset it, but it does the same thing. The compressor is 1 1/2 yrs. old, but has only been used about 3 times.
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If the pump turns easily by hand and trips breaker, most likely the start capacitor is weak or bad. If the pump is hard to turn by hand then problem is most likely the in-tank check valve is leaking pressure back to the pump causing the motor to overload. If the pump turns easily by hand and the check valve is good and capacitors are good, then use amp gauge to verify overload, if amp gauge shows normal amp draw then most likely weak reset button. Good luck
The button is a current overload protection for the motor. There is a variety of causes. Defective motor windings, carbonized burnt pressure switch contacts, loose connection (e.g. cord to plug, switch terminals, motor terminals), wrong voltage supply to the motor, worn motor bearings, drive belt too tight, or defective driven machine.
I would run the motor with no load, remove the belt or coupling to the compressor pump, and read the amperes and compare to the motor nameplate rating, let it idle a few minutes and listen for bearing noise. By reading motor amperes or current while the compressor is still connected to the motor, it can be determined if the reset button/overload protector is weak. Check every electrical connection for discoloration or overheating and repair if any are found. Check the contacts of the pressure switch. If nothing wrong is found and the motor is just overdrawing current or amperes, then it is time to replace the motor, probably due to a weak or defective motor internal winding.
If it doesn't try to start, then it could be the pressure switch. Another suspect could be the thermal overload on the motor. The motor (or just the overload) might be overheating and shutting the unit off, then allowing it to restart when it cools.
Is there any humming, or does it blow the breaker? When ot shuts off, do you hear a brief hiss of air?
If there is humming or breaker blowing on restart, or no hiss of air at shutoff, the pressure switch unloader valve is probably bad. If the air blows off, and there is no humming, and the compressor doesn't reliably start, it is probably the pressure switch. If pressure drops too low, give the pressure switch a tap with a screwdriver. If it starts then, the pressure switch is your problem.
The first thing to check is the thermal protector (circuit breaker). It is a small black button mounted on the housing on the back side of the pump motor. The unit will have to cool down before the button will reset. Usuall causes for the thermal protector to pop are: running the compressor on an extension cord, running the compressor on power lines or circuits that can't carry enough amps to run the motor, or little or no oil in the compressor causing excessive friction and heat buildup. If the thermal protector isn't tripped the next thing to check is the pressure switch. If the springs inside are broke or damaged they won't trip the switch to turn the compressor on. If the capacitor(s) are bad the motor will hum and/or try to turn but not have the power to start spinning.
the humming is coming from the motor,if you can spin the drum by hand and it moves freely you need to replace the motor,if it's hard to move you need to take the dryer apart to see why it's hanging up,the overload resets on the motor that's why after a while you'll hear the hum again,if you hold the button to long you'll pop the overload
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