Manitowoc Ice UNDERCOUNTER QM30 - Manual (Page 15)

Part Number 000001772 07/08 3-1
Section 3
Operation
Sequence of Operation
*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.
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.
Ice Making Sequence
of Operation
Control Board Relays
1
Compressor
2
Hot Gas Valve
Water Fill Valve
3
Water Pump
Fan Motor
Length of
“ON” Time
Start-Up*
1.Water Purge
2.Refrigeration
System Start-Up
off on on
2.9 Minutes
(175 Seconds)
on on off 5 Seconds
3.Freeze Cycle
on off on
Automatically deter-
mined
4.Harvest Cycle
on on off
Automatically deter-
mined
5.Auto Shut-Off
off off off
Until bin thermostat
re-closes