Test the compressor motor for continuity using a multitester. Set the multitester to the ohms setting X1.
Place one probe on any terminal and then touch the other probe to each of the other two terminals. The multitester should display a reading of roughly zero ohms.
Now move the first probe to a different terminal and test the other two terminals with the other probe. Finally, move the first probe to the last terminal and test each of the other terminals with the other probe. Every test should have continuity with the multitester displaying roughly zero ohms. If the compressor motor does not pass all of these tests, the compressor will require professional service.
Now test the compressor for ground. With the multitester still set to X1, touch one probe to bare metal on the compressor housing (it may be necessary to scratch away a little paint to expose the metal). Touch the other probe to each of the three terminals in turn.
None of the terminals should have continuity; the multitester should display a reading of infinity. If any of the grounding tests show continuity, the compressor will require professional service.