Manitowoc CNF0201, Technician'S Handbook

Page: 90 / 120

90 Part Number 000015432 Rev02 5/21
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.
Check Motor Windings to Ground
Check continuity between all three terminals and the
compressor shell or copper refrigeration line. Scrape metal
surface to get good contact. If continuity is present, the
compressor windings are grounded and the compressor
should be replaced.