Compressors take the refrigerant charge in your unit, compress it and then pump it out to cool down the fridge and freezer. If the motor, coils or fan break down, so does your fridge's ability to keep your food fresh and frozen. There are many signs that a compressor has failed and will need repair or replacement.
Refrigerator Makes Loud Clicking Sounds
If your refrigerator is making loud clicking sounds, it is likely that the compressor is overheating and turning itself off as a safety measure. The compressor has a start/stop switch to perform this action, which produces the clicking sound. It is also possible, though less likely, that the switch itself is bad.
Refrigerator Turns On and Off Continuously
If your refrigerator keeps cycling on and off every few minutes, you likely have a bad condenser coil, condenser fan or condenser motor.
Refrigerator Isn't Cold Inside, But It Is Running
This indicates that your compressor is functioning, but it may not be functioning well enough to keep the refrigerator cool. This can also mean the refrigerator no longer has adequate refrigerant for the compressor to operate well, requiring the refrigerant to be replenished or replaced.
Refrigerator Does Not Run
If the refrigerator light is working, but the refrigerator isn't cool enough and never sounds like it's running, it could be the compressor. But since replacing a compressor is much more expensive than fixing other reasons a refrigerator might not be getting cold, be sure to check for other causes. Perhaps someone turned the temperature up, or the temperature control or the starter relay have failed.
Refrigerator Runs Much More Than It Used To, But Isn't As Cold
If the refrigerator just runs and runs--as indicated by the loud sound of the motor--but isn't cooling off, you may need a new condenser. This problem could also be caused by a bad condenser or evaporator fan.
Frost Builds Up In Refrigerator
If your freezer begins to have unusual amounts of ice buildup, this can indicate that a new condenser is needed.
Testing the Compressor Motor
Before testing the compressor motor, it is very important that you unplug your refrigerator. These appliances have a lot of amperage going through them, so you can be seriously injured or killed by an electric shock if you test the compressor motor while the refrigerator is on. It is also critical that you know whether your refrigerator has a capacitor, which stores energy even when the unit is off. If you have lost your owners manual or otherwise can't verify that there is no capacitor, do not attempt to test the compressor motor.
You will need a multimeter, a small hand-held device that tests resistance and voltage, to perform this test.
Locate the compressor on the bottom back of your unit. It will have a metal panel over it. If you can't locate it, see resources below for images of compressors. Remove the metal panel, which is held on with a clip. You will see a device with copper wiring wrapped around it, which is the compressor relay. Simply pull this straight out. You will see three terminals.
Get your multimeter and set it to X1. Touch the first probe of the multimeter to any terminal, then touch another terminal with the second probe. You should get an ohm reading of zero. Any other reading means it's time to call in a professional to repair the refrigerator. Test each terminal, to verify that each reads zero.
Now test the ground. Touch one probe to the metal housing of the compressor, and the other to each of the terminals in turn. You should get the infinity sign reading, indicating a ground is present. Any other reading and, again, you need to call a professional to repair the refrigerator.