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MC0322 through MC2148
Air, Water, and Remote Cooled Service Manual
How It Works - Remote
Freeze Cycle. At start up the controller drains and refills the reservoir. The reservoir refills when the mid length
water level sensor probe is uncovered and continues to fill until the top probe is in contact with water. When
the reservoir has filled, the liquid line valve, compressor and water pump are switched on. After the discharge
pressure has increased past the set point of the headmaster in the condenser, the headmaster will direct
refrigerant gas into the condenser and warm air will be discharged out of the condenser. The headmaster will
modulate to maintain a minimum discharge pressure. Water flows over the evaporator as the refrigeration
system begins to remove heat. When the water temperature falls to a preset point, as measured by the water
temperature sensor, the controller shuts off the water pump for 30 seconds. The freeze cycle resumes when
the pump restarts and ice begins to form on the evaporator. As it forms, the water flowing over the ice moves
closer and closer to the metal tip of the ice thickness sensor. When it comes into contact with the sensor for a
few continuous seconds, that signals the controller that the freeze cycle is complete.
Harvest Cycle. When the harvest cycle begins, the controller switches on the hot gas valve, and through a
parallel circuit, the harvest assist solenoid. After a few seconds the purge valve opens and water is drained
from the reservoir. Based on either the automatic purge or manual purge setting, the pump and purge valve
will be switched off at a time determined to have drained enough water for that setting. The inlet water valve
will open to fill the reservoir anytime the mid length probe is uncovered, which occurs during the reservoir drain
cycle.
Harvest continues as the hot discharge gas flows into the evaporator serpentine, heating up the evaporator. At
the same time the harvest assist solenoid is pushing against the back of the ice slab. When the ice releases
from the evaporator, it harvests as a unit, and the harvest assist probe provides some additional force to push
it off. When the ice falls off it will force the curtain(s) open. An open curtain during the harvest cycle signals
the controller that the evaporator has released its ice. If this is a single evaporator machine the controller will
terminate harvest. If it is a two evaporator machine, the controller will continue harvest until both curtains have
opened. If a curtain remains open, the controller will shut the machine down. Anytime harvest is complete the
hot gas valve and harvest assist are shut off.
The harvest assist pin returns to its normal position by spring pressure.
If the curtain(s) re-close after harvest, the freeze cycle will restart.
Shut down occurs when a curtain remains open after a harvest cycle. The controller will switch off the liquid
line solenoid valve and operate the compressor for 30 seconds, then shut it off.
January 2022
Page 19
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