Refrigeration Diagnostics - Manitowoc QM20 Technician's Handbook

REFRIGERATION DIAGNOSTICS

QM20
The QM20 ice machines have a very small refrigerant
charge, 4.59 oz (130 g) and we do not recommend
diagnosing the ice machine using refrigerant pressures. For
this reason we have not included refrigeration access fittings.
Verify that your water flow is even across the entire
evaporator before diagnosing the refrigeration system.
Mineral build-up on the evaporator assembly can cause
water tracking and an erratic ice fill pattern. Clean with
Manitowoc Ice Machine cleaner to remove any mineral build-
up before entering the refrigeration system.
The following can be used for diagnostics:
Capillary Tube failures or low refrigerant charge will always
result in a starving evaporator.
Assume 86°F (30°C) air temperature 68°F (20°C) water
temperature.
Suction line temperature at the compressor will range from
86°F (30°C) three minutes into the cycle to 8°F (-13°C) at the
end of the freeze cycle. An obstructed capillary tube or low
refrigerant charge will have a suction line temperature higher
than normal.
Discharge line temperature at the compressor will range from
168°F (76°C) to 140°F (60°C) through the freeze cycle. An
obstructed capillary tube or low refrigerant charge will have a
lower discharge line temperature than normal.
Suction line temperature at the compressor will range from
64°F (18°C) to 111°F (44°C) through the harvest cycle. An
obstructed capillary tube will not affect suction line
temperature range during the harvest cycle. Low refrigerant
charge will have a lower temperature than normal.
Discharge line temperature at the compressor will range from
180°F (82°C) to 150°F (60°C) through the harvest cycle. An
obstructed capillary tube will not affect discharge line
temperature range during the harvest cycle. Low refrigerant
charge will have a lower temperature than normal.
Ice fill pattern will vary depending on severity of the
obstruction or refrigeration loss. Ice fill patterns will range
from no ice on the entire evaporator to thin only at the
evaporator outlet (thin at the bottom, thick at the top of the
evaporator).
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