Manitowoc Ice QM45 Series - Manual (Page 18)

Ice Machine Operation Section 3
3-2
Ice Making Sequence of Operation
INITIAL START-UP OR START-UP AFTER
AUTOMATIC SHUT-OFF
1. Pressure Equalization
Before the compressor starts the hot gas valve is
energized for 15 seconds to equalize pressures during
the initial refrigeration system start-up.
2. Refrigeration System Start-Up
The compressor starts after the 15-second pressure
equalization, 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 a relay. As a result, any time the relay 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 starts after the 30-second Prechill.
An even flow of water is directed across the
evaporator and into each cube cell, where it freezes.
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. Harvest
The water pump de-energizes stopping flow over the
evaporator. The rising level of water in the sump
trough diverts water out of the over flow tube,
purging excess minerals from the sump trough. The
hot gas valve also opens to divert hot refrigerant gas
into the evaporator.
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 contacts
the ice damper, 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 ice
damper and will hold it down. After the ice damper is
held open for 7 seconds, the ice machine shuts off.
The ice machine will remain 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 damper. As the ice damper 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.