Manitowoc UG Series, Technician'S Handbook

Page: 54 / 128

54 Part Number: 040006847 12/19
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.
COMPRESSOR DRAWING HIGH AMPS
The continuous amperage draw on start-up should not be
near the maximum fuse size indicated on the serial tag.
The wiring must be correctly sized to minimize voltage
drop at compressor start-up. The voltage when the
compressor is trying to start must be within ±6% of the
nameplate voltage.
COMPRESSOR DRAWING LOCKED ROTOR
The three likely causes of this are:
• Low voltage supply (check voltage while compressor is
trying to start),
• Defective starting component,
• Mechanically seized compressor.
To determine which you have:
• Install high and low side gauges,
• Try to start the compressor,
• Watch the pressures closely.
If the pressures do not move, the compressor is seized.
Replace the compressor. If the pressures move, the
compressor is turning slowly and is not seized. Check the
capacitors and relay.