Capacitors Parallel or Series Wired?

The motor will run without a run cap, only a little less powerful. In post #1 you said the motor wouldn't move at all when the failure occurred.
Was it totally silent or did it hum?
Clearly you need a new run cap- and you might have an intermittent connection someplace. Capacitor start motors have an internal start switch
which can and does burn out eventually- you might have to open up the motor at some point and service that switch.
But if the motor is totally silent when the failure occurs then that would indicate power not reaching the motor.

The best way to troubleshoot intermittents is if you can get it to fail right in front of you, with a diagram of the wiring already in hand or head. Then you go point by point with your volt meter until you find the break.
 
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Air conditioning supply shops stock capacitors... they go out regularly on AC units.

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While your in there might as well check and clean the motor starter contacts. I've had that issue before. Mike
 
I ordered a capacitor tester, I seem to need one a lot with the phase converters. If the run capacitor is still viable, I will check its value to see what to replace it with. If not, I will steel wool it and try to read some numbers. If it does that again, I’ll bypass or replace the thermal switch, but it fired right up today. I have not had the compressor long. It’s a T30 Ingersoll Rand. All it cost me was a haul bill and new controls.The motor starter came from a guy on here and he had cleaned the contacts before mailing it to me. Thanks for the ideas. I have several run capacitors, may have the right value on hand if I knew it.
 
Check the run cap again with your regular ohmmeter- shorted caps usually stay shorted
But the run cap only helps the efficiency of the motor, it will run without it
 
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I had not tested the run capacitor with ohm meter disconnected from motor. Did this today . It showed resistance, then went to zero (or infinity ) on the digital meter. Got the capacitance meter today from USPS. it shows 17 MFD. That seems really small for a 7.5 to 10 HP motor. Is that possible? No numbers on it but Mallory C8000 AC and 8016-6.
 
It's probably fine- run caps are usually much smaller than the start ones.
If it had been working before then it's likely ok, even if it has lost some value.
Did you notice when it failed the first time whether the motor was humming?
That would be a clue as to whether it's a cap failure or a bad connection
 
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Those Mallory numbers do not pull up any capacitors. Run capacitor should have a metal shell for an oil filled capacitor, I would expect to be in the 50-70uF range minimum voltage 370VAC for 7.5 Hp motor.
 
It did buzz, not sure if that was the motor starter or the motor. The motor starter for sure humms. The run capacitor is oil filled metal can. I really just wanted to establish the correct MFD value while it was still running to know what to replace it with later. I have some 70 MFD capacitors I can try if it quits again. I guess the 16 in the 8016 number could be 16 MFD.
 
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