156 Part Number: 000015431 Rev01 5/19
COMPRESSOR ELECTRICAL DIAGNOSTICS
The compressor does not start or will trip repeatedly on
overload.
Check Resistance (Ohm) Values
NOTE: Compressor windings can have very low ohm
values. Use a properly calibrated meter.
Perform the resistance test after the compressor cools. The
compressor dome should be cool enough to touch (below
120°F/49°C) to assure that the overload is closed and the
resistance readings will be accurate.
SINGLE PHASE COMPRESSORS
1. Disconnect power then remove the wires from the
compressor terminals.
2. The resistance values between C and S and between
C and R, when added together, should equal the
resistance value between S and R.
3. If the overload is open, there will be a resistance
reading between S and R, and open readings between
C and S and between C and R. Allow the compressor
to cool, then check the readings again.
THREE PHASE COMPRESSORS
1. Disconnect power and remove the wires from the
compressor terminals.
2. The resistance values between L1 and L2, between L2
and L3, and between L3 and L1 should all be equal.
3. If the overload is open, there will be open readings
between L1 and L2, between L2 and L3, and between
L3 and L1. Allow the compressor to cool, then check
the readings again.
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