Scotsman CME256 AutoIQ - Manual (Page 16)

Technicians Only: Freeze Cycle Operational Sequence
Assuming the machine has been operational, the
Freeze cycle begins with the end of the Harvest
Cycle:
•
Reservoir is full
•
Condenser fan is OFF
•
Water Inlet Valve is OFF
•
Water Pump is ON
•
Compressor is ON
•
Hot Gas Valve is ON
Controller Operation, Beginning freeze:
1. Switches on the Freeze indicator light and shuts
off the hot gas valve.
2. Measures and stores the discharge
temperature.
3. Starts the fan motor (air cooled only). Some
early units have a fan control switch, it shuts the
fan off if the discharge pressure drops below 190
PSIG. Machines built beginning in August 1996 do
not have a fan control switch, instead the
Controller checks the discharge temperature and
cycles the fan every 30 seconds if the temperature
is low (below 125oF. or more than 3381 ohms).
If the discharge temperature exceeds the design
maximum (250oF. or less than 377 ohms), shuts
the machine down on a Refrigeration Error.
4. Checks for a “bin full" signal throughout the
cycle.
5. Measures the reservoir water temperature. If the
machine is operating correctly, the reservoir water
temperature will fall at a standard rate. The
Controller will be checking to see if the water
temperature fall matches that rate.
If not, it re-checks the discharge line temperature.
If too low, it Shuts Down on a Refrigeration Error.
If the discharge temperature is acceptable, the
water system is checked by shutting off the water
pump and determining if the water level goes up
enough. If it does not, it is assumed that there is a
water pump problem and the machine Shuts Down
on a Water Error.
If the water level does “measure up" the water
pump is restarted and the controller then
measures how long it takes to lower the water
level. If the water level does not fall, the machine
Shuts Down on a Water Error.
6. Once per cycle the machine may shut off the
water pump. It only does this when the water
temperature reaches a preset minimum (38oF. or
27835 ohms). The pump will only be off for a few
seconds. After the pump restarts, the inlet water
valve opens to refill the reservoir.
7. As the machine makes ice, the water level in the
reservoir will ultimately fall to the Harvest Level
(when the top electric eye in the water level sensor
is disrupted by the adjustment screw).
Note: If the freeze cycle exceeds the preset
Maximum (50 minutes), the Controller will Shut
Down on a Refrigeration Error.
8. The end of Freeze cycle will see the machine in
this state:
•
Water level = below harvest position
•
Condenser fan will be off
•
Water inlet valve will be off
•
Water pump will be ON
•
Compressor will be ON
•
Hot gas valve will be off
At this point Harvest begins and the Controller
switches the Harvest indicator light ON.
Note: If there is a power interruption, the system
controller will automatically restart the machine
with a process that begins with getting the
machine back to a normal state: water re-fills, the
unit freezes for 30 seconds and then goes into a 4
minute harvest. It will then proceed to a new
Freeze cycle. While in an electrical restart mode,
the controller’s Freeze light will be blinking - even
when the machine is in harvest.
CME256, 506, 656, 806: AutoIQ™ Cubers
July 2002
Page 16