Manitowoc Ice Q 800 - Manual (Page 14)

Ice Machine Operation Section 3
3-2
Ice Making Sequence of Operation
Initial Start-Up Or Start-Up After Automatic
Shut-Off
1. Water Purge
Before the compressor starts, the water pump and
water dump solenoid are energized for 45 seconds to
purge the ice machine of old water. This ensures that
the ice-making cycle starts with fresh water.
The hot gas valve is also energized during the water
purge, although it stays on for an additional 5
seconds (50 second total on time) during the initial
refrigeration system start-up.
2. Refrigeration System Start-Up
The compressor starts after the 45-second water
purge, and remains on throughout the entire Freeze
and Harvest Sequences. The hot gas valve remains on
for 5 seconds during initial compressor start-up and
then shuts off.
At the same time the compressor starts, the condenser
fan motor (air-cooled models) is supplied with power
throughout the entire Freeze and Harvest Sequences.
The fan motor is wired through a fan cycle pressure
control, therefore it may cycle on and off. (The
compressor and condenser fan motor are wired
through the contactor. As a result, any time the
contactor coil is energized, the compressor and fan
motor are supplied with power.)
FREEZE SEQUENCE
3. Prechill
The compressor is on for 30 seconds prior to water
flow to prechill the evaporator.
4. Freeze
The water pump restarts after the 30-second prechill.
An even flow of water is directed across the
evaporator and into each cube cell, where it freezes.
The water fill valve will cycle on, then off one more
time to refill the water trough.
When sufficient ice has formed, the water flow (not
the ice) contacts the ice thickness probe. After
approximately 7 seconds of continual water contact,
the harvest sequence is initiated. The ice machine
cannot initiate a harvest sequence until a 6-minute
freeze lock has been surpassed.
HARVEST SEQUENCE
5. Water Purge
The water pump continues to run, and the water
dump valve energizes for 45 seconds to purge the
water in the sump trough.
After the 45 second water purge, the water pump and
dump valve de-energize. (Refer to “Water Purge
Adjustment” for details.)
The hot gas valve also opens at the beginning of the
water purge to divert hot refrigerant gas into the
evaporator.
6. Harvest
The hot gas valve remains open and the refrigerant
gas warms the evaporator causing the cubes to slide,
as a sheet, off the evaporator and into the storage bin.
The sliding sheet of cubes swings the water curtain
out, opening the bin switch.
The momentary opening and re-closing of the bin
switch terminates the harvest sequence and returns
the ice machine to the Freeze Sequence (steps 3 - 4).
AUTOMATIC SHUT-OFF
7. Automatic Shut-Off
When the storage bin is full at the end of a harvest
sequence, the sheet of cubes fails to clear the water
curtain and will hold it open. After the water curtain
is held open for 7 seconds, the ice machine shuts off.
The ice machine remains off for 3 minutes before it
can automatically restart.
The ice machine remains off until enough ice has
been removed from the storage bin to allow the ice to
fall clear of the water curtain. As the water curtain
swings back to the operating position, the bin switch
re-closes and the ice machine restarts (steps 1 - 2),
provided the 3-minute delay period is complete.