Compressor Electrical Diagnostics - Manitowoc UG080A 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 49°C) to assure that the overload is
closed and the resistance readings will be accurate.
Single Phase Compressors
1. Disconnect power from the condensing unit and
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.
To determine if the Compressor is seized check the
amp draw while the compressor is trying to start.
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