Testing and replacing a refrigerator's compressor relay is not a typical job for the do-it-yourselfer. But, for someone who is willing to try their best to figure out a problem in lieu of purchasing a new refrigerator, the time could be well spent indeed. For those with the guts and determination, here is how to test your refrigerator's compressor relay.
Before working on your refrigerator, always unplug the unit or turn off the circuit breaker that powers it.
Locate the compressor. It is usually large and cylindrical, and at the bottom rear of the refrigerator. On the right side of the compressor you should see a box with wires coming out of it. In this box is where the compressor relay is.
Note that some older refrigerators use a capacitor with their compressors. If yours has a capacitor wired to the compressor, it will need to be discharged prior to working on the unit. Take your 20-amp wire wound resistor, available at most specialty electronics stores, and touch the leads of the resistor to the terminals on the capacitor. This will remove any retained voltage and eliminate the risk of backcurrent shock.
Remove the cover on the compressor relay box. The cover is usually held in place by retaining clips or tension clips. There are usually three components inside this box -- the compressor relay, the compressor motor terminals and the overload protector. The compressor relay is the largest component and will either be wirewound or solid state. If the part is solid state, then you will have to have a professional test the part, as it requires specific equipment for testing. If you have a wirewound relay, pull it straight off of the compressor.
Use a pair of needlenose pliers to pull the connector off the relay's terminal. Be sure to pull it off by grasping the connector, NOT the wire. Check both the wire connector and the compressor relay for any signs of corrosion.
Dust off the relay and take a good look at it. You should see two plug-type terminals marked "S" and "M" and the slip-on terminal marked "L."
Set your multitester, available at any home improvement store or specialty electronics store, to read ohms -- usually the X1 or RX1 setting. Set the relay on a flat surface so that the "S" and "M" terminals are on the bottom.
Insert one probe of the tester in the "S" terminal and one in the "M" terminal. The tester should read "zero" ohms. Keeping the probes inserted in the terminals, turn the relay over. You should hear an audible "click" and the tester's reading should change from "zero" to "infinity."
Turn the relay back over. Now, touch one probe to the "S" terminal and the other probe to the "L" terminal. The tester should read "zero" ohms. Turn it over again, with the probes still on the terminals, and the tester should read "infinity."
Turn the relay back over. Now, touch one probe to the "M" terminal and the other to the "L" terminal. The tester should read "zero" ohms. Turn the relay over with the probes still in place and the tester's reading should not change -- it will remain at "zero" ohms.
If the compressor relay passes this series of tests, then the relay is not the problem with your refrigerator. If it fails any one of these tests, take it to an appliance parts shop and purchase a replacement.
Return everything to its original place in the fridge. Be sure to remove the 20-ohm resistor from the capacitor before plugging the refrigerator back in.