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Re: Air compressor starts slowly and then trips 20 amp...
Is it 220 or 110 ? How many horse power is it but most importantly is how many amps is the motor itself? If it is 15 amps let's say then that doesn't leave much more for anything else to be running on the same circuit of which you have the compressor plugged into. While 110 is more convenient, I know that is my preferred choice, when you get to 3 HP or over size motors your looking at close to or right at 15 amps of supply needed. Could also be the breaker needs replacing. Hope this helps.
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Rmove the drive belt and check the motor. It should turn very freely by hand and if turned on should start up easily. If it turns hard check the armature bearings if it starts slowly but turns OK after you give it a push, you have a bad start capacitor. If the motor is OK check the pump. It should turn fairly freely except on the compression stroke where you should feel slightly more pressure is needed to turn it. If you can't turn the flywheel or it turns very hard, you should check the connecting rod to crank shaft joint and crank shaft bearings. These usually go bad if there is low or no oil in the crank case.
Does it make any noise at all? If not, check the motor for a protective device. A thermal reset would be a red button on the end of the motor. It may be as simple as that.
If it hums loudly, and turns over by hand- no power applied- with difficulty the motor bearings or compressor bearings may be needing attention.
If it hums loudly and barely turns, but turns by hand freely, the motor has a start/run capacitor- it likely failed. Replacing the capacitor is a simple task- just make sure to replace it with one of similar ratings.
first,with power off,try to manually turn the fan by hand,it should turn freely and coast to a stop by itself,then if so,there is what they call a "dual-Capacitor" inside the unit and one side of this capacitor is the motor start/run capacitor and they go bad,it is a silver can with 3 terminals marked F/C/H fan/common/hermetics (for the compressor), and will say something like 5uf./35uf at 440 volts A.C. on the body of this component go get a replacement at most electrical outlets
Shut the power off to the unit, spin the fan blade to see if it spins freely. If it doesn't spin freely, (there appears to be a little drag when you spin it),the bearings are bad, if it does spin freely, then try moving the motor shaft from side to side if there’s any play in the shaft side to side then the bearings are worn and motor needs replaced. Then, check the capacitor, if it’s bulging even slightly, the capacitor is bad and needs replaced. Most of the time people replace the capacitor if motor seems ok. If capacitor is ok, turn power on to see if the motor is getting the proper voltage, if it is and not trying to run, then the windings are probably open, the motor's bad and needs replaced.
Air compressors tend to draw more power as they age, however, will not trip breaker unless some malfunction. Here are some simple tests. Unplug compressor and turn the pump by hand, you may have to remove a cover to do this. It should turn freely; any resistance could be failing bearing (would make noise) unloader/check valve leaking allowing back pressure to pump, or failed start capacitor/start winding. Easy test for checkvalve. With pressure in tank loosen discharge hose at tank and check for air leak. Check valve should hold pressure in tank. Replace as needed. Failed capacitor/s will cause high amp draw. Remove from circuit and test. UF reading should be within 95% of printed rating. Finally, most air compressor motors have two windings, start and run. Power to windings is controlled by flyball switch inside rear of motor. This switch has contacts that can stick in start position and cause high amp draw. Examine windings for signs of overheating. Copper windings generally have color of new penny. Very dark brown windings bad news. Gook luck
It is a good sign that the motor turns freely with and without air. That indicates that you have good bearings and that the intank check valve is in good condition. Next you should check the capacitors and the condition of the windings. Some motors have start and run capacitors and others only have run cap. Remove from the circuit and test with meter having cap. test setting. Most shops will test them for free. The cap should test within 95% of stated ( uf ) value. Replace as needed. Finally check that the flyball switch at rear inside of motor is functioning correctly. At rest, switch is at start winding, then a split second after start, it shifts to run winding. Check contacts are not stuck and that switch is working and lastly that the winding are the color of new penny. Good luck.