Scotsman C2648 - Manual (Page 28)

C2648 Prodigy and Prodigy Plus Service Manual
January 2015
Page 28
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 assists 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 assists 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.