Capacitor Run Motor

This is getting to be way too much work to pump up tires!

Thanks for your help.

The purpose of a start capacitor is to shift the current 90 degrees ahead of the voltage (or at least that would be the optimal shift).

The purpose of a run capacitor as stated before, is to correct the power factor. This lowers the amperage draw of the motor and increases efficiency.

If you happen to have a decent fluke or equivalent meter you can test the capacitance to be sure the capacitor hasn"t changed in value due to a loss of electrolyte.

You can also test for a defective capacitor using an ohmmeter. Place one test lead on each side of the capacitor.

- If Fauly -
The meter will stay at 0 (shorted capacitor)
The meter will stay at infinity (open capacitor)

- If Good -
The meter will temporarily read zero (or near zero) but then gradually climb towards infinity

*To repeat the test reverse the two leads of the meter

You're correct that the smaller capacitor is the run capacitor. You're also correct that a defective run capacitor could cause the motor to stall out under normal load. I'd replace the 35 mfd capacitor and see what happens. That is, assuming that the compressor was working fine before. If you just installed the compressor, I'd check the voltage to the motor under load to make sure you don't have a voltage drop somewhere.

You'll probably have to take a chance, and replace it, although there is no guarantee that will solve your problem.

Do you have a good power supply to the motor, without any long and/or undersized extension cords?