How to Check The Winding Resistance of a 3ph Compressor

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The first step is to always be safe when using an electrical meter. When checking any compressor winding make sure you lock out and tag out the unit before any work is done. Make sure you always verify there is no voltage at the compressor before you remove the leads.

Here are the steps in checking the windings of a compressor:

Step 1: Read the compressor manual for that compressor to understand if there are any special safety devices that can affect the windings
Step 2: Lockout/Tagout the compressor and unit
Step 3: Verify there is no power at the compressor
Step 4: Remove wire leads or molded plug from compressor
Step 5: Find out what the resistance should be on Copeland Mobile for that model of compressor
Step 6: Put multimeter on ohms
Step 7: Check and write down resistance from L1-L2, L1-L3, L3-L2
Step 8: Check resistance from L1 to Compressor Ground, L2 to Compressor Ground, L3 to Compressor Ground.
Step 9: Compare findings to actual from Copeland Mobile
Step 10: If compressor windings open make sure to let the compressor cool as a safety device or the overload could be open
Step 11: If you determine the compressor is failed, now its time to find out what mechanical failure caused it

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Megohm Values of Copeland® Compressors –