Compressor Electrical Diagnostics; Check Resistance (Ohm) Values; Single Phase Compressors; Three Phase Compressors - Manitowoc S300 Technician's Handbook

COMPRESSOR ELECTRICAL DIAGNOSTICS

The compressor does not start or will trip repeatedly
on overload.

Check Resistance (Ohm) Values

Compressor windings can have very low ohm
NOTE:
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.
92 Part Number 80-1479-3 7/10