Manitowoc Ice QM20 - Manual (Page 15)

Section 3 Ice Machine Operation
3-1
Section 3
Ice Machine Operation
Sequence of Operation
Control Board Relays
Ice Making
Sequence of
Operation
1
Compressor
2
Hot Gas Valve
Water Fill Valve
3
Water Pump
Fan Motor
Length of
“ON” Time
Start-Up 1
1. Water Purge
Off On Off
2.9 Minutes
(175 Seconds)
2. Refrigeration
System Start-Up
On On Off 5 Seconds
3. Freeze Cycle On Off On
Automatically
determined
4. Harvest Cycle On On Off
Automatically
determined
5. Auto Shut-Off Off Off Off
Until bin thermostat
re-closes
1 Initial Start-Up or Start-Up After Automatic Shut-Off
INITIAL START-UP OR START-UP AFTER
AUTOMATIC SHUT-OFF
1. Water Purge
The water fill valve and the hot gas valve are
energized for 2.9 minutes (175 seconds). This
ensures that the ice making cycle starts with fresh
water, and that the refrigerant pressures are
equalized prior to refrigeration system start-up.
2. Refrigeration System Start-Up
The compressor starts 2.9 minutes (175 seconds)
after the water fill valve and hot gas valve are
energized. (The water fill valve and hot gas valve
remain energized for 5 seconds during compressor
start-up, and then shut off.) The compressor remains
on throughout the entire freeze and harvest cycles.
3. FREEZE CYCLE
The condenser fan motor and water pump are
energized and remain on throughout the entire
freeze cycle. An even flow of water is directed
across the evaporator and into each cube cell, where
it freezes.
The control system automatically determines the
length of the freeze cycle by monitoring the
temperature of the refrigeration system liquid line.
4. HARVEST CYCLE
The condenser fan motor and water pump de-
energize. The water fill valve energizes to purge the
water in the water trough. The hot gas valve also
energizes at the beginning of the harvest cycle to
divert hot refrigerant gas into the evaporator. The
hot refrigerant gas warms the evaporator, causing
the cubes to slide, as a sheet, off the evaporator and
into the ice storage bin.
The control system automatically determines the
length of the harvest cycle, based on the
temperature of the refrigeration system liquid line at
the end of the freeze cycle. At the end of the harvest
cycle, the ice machine returns to another freeze
cycle (step 3, above).
5. AUTOMATIC SHUT-OFF
The ice machine shut-off is controlled by the level
of ice in the ice storage bin. When the bin is full, ice
cubes contact the bin thermostat bulb holder, which
cools down and opens to stop the ice machine. The
ice machine remains off until enough ice has been
removed from the bin. This causes the thermostat
bulb holder to warm and close, restarting the ice
machine. When the ice machine restarts, it returns
to the start-up sequence (steps 1 and 2, above).