Manitowoc QD0202A, Service Manual

Page: 51 / 175

Part No. 80-1100-3
4-1
Section 4
Ice Machine Sequence of Operation
Self-Contained Air- and Water-Cooled
Q200/Q280/Q320/Q370/Q420/Q450/Q600/Q800/Q1000/Q1300/Q1600/Q1800
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
completely purge the ice machine of old water. This
feature ensures that the ice making cycle starts with
fresh water.
The harvest valve(s) is also energized during water
purge, although it stays on for an additional 5 seconds
(50 seconds 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 it remains on throughout the entire Freeze and
Harvest Sequences. The water fill valve is energized at
the same time as the compressor. It remains on until the
water level sensor closes for 3 continuous seconds, or
until a six-minute time period has expired. (See “Water
Inlet Valve Safety Shutoff,”
Page 6-50 .) The harvest
valve(s) 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, anytime 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 and 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.
Figure 4-1. Freeze Sequence
(Typical Q450 Shown)
Continued on next page …