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Open Compressor Windings

To determine if compressor windings are open or shorted, perform this simple test.

  • Measure the Ohms across 3 compressor terminals using an open continuity setting on your multimeter
    • Common to Run should have the lowest resistance
    • Common to Start should have the 2nd largest resistance
    • Run to Start should have the largest resistance
  • In all single-phase instances the value from Run to Start should equal the sum of the values from Common to Run and Common to Start
    • R:S = C:R + C:S
  • On a 3-phase compressor the resistance values should be within 3% of each other across each of the terminals
    • It is not necessary to wire the harness up to the Common, Start and Run terminals exactly because the compressor will start regardless.

Q: Do open winding readings mean a defective compressor?

A: No, not necessarily. If the internal overload protector opened, leave enough time for it to reset before checking the valves. An open overload protector could give the same readings as open windings, leading to a misdiagnosis and the condemnation of a good compressor.

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