Compressor Won't Start due to Mis-Wired Contactor

Replaced the Contactor - Now Compressor Won't Start

Issue: The compressor was operating before replacing the contactor, but now it just hums and won't come on.

Cause: This is generally the result of mis-wiring the high voltage going to the compressor.

Proper Wiring:

• One leg of the "load" side of the contactor should go directly to "C" (or Common) of the compressor.
• The opposite leg of the "load" side of the contactor should go to "R" (or Run) of the compressor.
• The same side that goes to "R" should also feed the "C" (or Common) terminal of the start capacitor.
• The "Herm" terminal of the capacitor should go to "S" (or Start) of the compressor.

It is not uncommon for the "R" of the compressor to feed from the "C" (or Common) of the capacitor instead of coming directly from the contactor. It doesn't matter as long as it comes from the opposite side that feeds the compressor "C".

Check Voltage:

If you feel that the wiring is correct but the compressor still hums and doesn't start, check voltage at the compressor terminals (if accessible).

• With the contactor pulled-in you should read 230V between C & R and 230V between C & S.
• There should be no voltage reading between R & S.