How It Works
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 pumps 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 evaporators 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 pumps
for 30 seconds. The freeze cycle resumes when the pumps restart 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 connects power to the High Capacity
Relay, which switches on the hot gas valves, and through a parallel circuit, the harvest assist solenoids.
After a few seconds the purge valve opens. When the purge valve is opened, a relay is energized to
disconnect power to pump number 2, and water is drained from the reservoir by pump number 1. 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's serpentines, heating up the
evaporators. At the same time the harvest assist solenoids are pushing against the back of each ice
slab. When the ice releases from an 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 that curtain open. An open
curtain during the harvest cycle signals the controller that that evaporator has released its ice. The
controller will continue harvest until all three 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
solenoid are shut off. The harvest assist solenoid pin returns to its normal position by spring pressure.
If the curtains 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.
November 2010
Page 5
C2648 Service Manual
