Get a Free Compressor Troubleshooting Guide – https://offers.refrigerationmentor.com/free-guide
It is very important to understand how to safely and properly check a compressor winding resistance with your ohmmeter. For single-phase compressors, you always want to check the winding resistance against the compressor electrical curve chart which you can get from the Copeland Mobile app and this will help you understand how the electrical motor is doing.
iOS – https://apps.apple.com/us/app/copeland-mobile/id789715706#?platform=iphone
Android – https://play.google.com/store/apps/details?id=com.emersonclimate.copelandmobile
Step 1 Always shut down, disconnect the power, make sure all sources of power are off and then lock it out safely.
Step 2 Verify with your meter that there is no power and it is safe to ohmmeter the windings.
Step 3 Scan or input compressor serial number into Copeland Mobile
Step 4 Recorded ohmmeter readings, C-S and C-R, and see if they match Copeland Mobile
Step 5 If you have an electrical problem like failed windings make sure to find the real issue that causes the electrical failure. Remember 80% of the time electrical failures are caused by mechanical issues.
Always check from the compressor terminals because if you check from the contactor and you get inconsistent readings it could be the contactor that has an issue, wiring that has an issue, terminal connections, or terminal insulator.
If you would like to know more about megohm values of a compressor check out this application engineering bulletin – https://webapps.emerson.com/online-product-information/Publication/LaunchPDF?Index=aeb&PDF=ae1294.pdf