Refrigeration System During Harvest; Water System; Control Sequence - Scotsman NW458 Service Manual

REFRIGERATION SYSTEM DURING
HARVEST
The refrigeration system performs the harvest
of ice by use of a hot gas bypass valve. When
the time comes to de-ice the evaporators, the
hot gas valve is energized, and the high
temperature, high pressure gas bypasses the
condenser, and is allowed directly into the
evaporator. The high pressure gas is cooled
by the cold evaporator so it condenses into a
liquid, giving up its heat as it does so. This
heat warms the evaporator and the ice frozen
onto the evaporator surface melts, releasing
the frozen cubes. Ice then falls by gravity into
the storage bin.
The liquid refrigerant goes through the suction
line into the heat exchanger where it boils-off
so that only refrigerant vapor is drawn into the
suction tube of the compressor.

WATER SYSTEM

During the harvest cycle, the electric water
drain valve is energized thereby opening the
drain line.
HARVEST (DEFROST) CYCLE
REFRIGERATION SYSTEM SCHEMATIC
All water remained in the reservoir at the end
of freezing cycle is pumped-out, to the waste,
through the water solenoid and drain line
during the first 40 seconds of the defrost cycle
eliminating any
accumulation of minerals concentration and
impurities in the water reservoir.
The water inlet valve is energized during the
last 10" of the operation of the water pump so
to rinse the water tank with new fresh water.
When the released ice cubes drop into the bin,
they open-up for a fraction of a seconds the
bottom end of plastic deflector.
This deflector swinging motion is enough to
reset the contact of the magnetic switch which
- via electronic control board de-energizes the
water drain valve allowing the unit to initiate a
new freezing cycle. The harvest cycle lasts
about 1.5-2 minutes.

CONTROL SEQUENCE

At the start of the freezing cycle, the contacts
of the magnetic switch mechanically operated
by the actuator plate of the deflector cover are
closed, thereby - via electronic control board -
20
possible build-up and