How to Test Single Phase Compressor for HVAC and Refrigeration Systems.
This test should only be performed by qualified HVAC technicians! Before you begin use your multimeter to ensure that power has been disconnected!
Testing the Compressor
Begin by testing the resistance of the windings. A single phase compressor will have three terminals. Common (C), Start (S) and Run (R).
1. Remove the wiring from the three terminals before testing.
2. Set your multimeter to read ohms.
3. Measure the resistance of common(C) and run(R). Record value. This should be your lowest resistance.
4. Measure the resistance between common(C) and start(S). Record value. Typically three to five times the resistance of (C)to(R).
5. Measure the resistance between start(S) and run(R). Record value. This value should equal the sum of the two previously recorded values.
If (C)to(R) and (C)to(S) equal (S)to(R) then the windings of the compressor are reading the proper resistance.
If (C)to(R) and (C)to(S) measure a resistance of infinity (OL) and (S)to(R) has a measurable resistance the the internal overload of the compressor has tripped. The overload provides protection to the compressor from excessive heat. If this is the case the compressor will most likely be extremely hot to the touch and will need to cool down before the compressor can be restarted.
The compressor should also be checked for resistance to ground. With the wiring still removed from the compressor terminals test the resistance of each terminal to ground. Ensure that your lead is making a solid connection to ground without any interference from dirt, paint, rust or any other debris. If no grounds are present you should read infinite (OL) resistance.