September 2008
Page 16
CU1526, CU2026, CU3030
Service Manual
How It Works - Air Cooled
Freeze Cycle.
At start up the controller operates the water pump and purge valve to drain the reservoir.
The float valve refills the reservoir after the purge valve shuts off. When the reservoir has filled, the
compressor and water pump start. After the discharge pressure has increased past the cut in point of the
fan pressure control, the fan motor(s) will begin to operate and warm air will be discharged. The fan
motor will switch on and off as the discharge pressure rises and falls. 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.
The controller may shut the air cooled fan motor off for a variable period of time to build up heat for
harvest. This is dependant upon the temperature of the discharge line sensor.
Harvest Cycle
. When the harvest cycle begins, the controller shuts off the fan motor, 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 float valve will open to fill the reservoir anytime 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 open. An open curtain
during the harvest cycle signals the controller that the evaporator has released its ice, and the controller
will terminate harvest. If the curtain remains open, the controller will shut the machine down on bin full.
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 curtain re-closes after harvest, the freeze cycle will restart.
