208 Part Number 80-1505-3 6/11
Harvest Cycle Operation
During the Harvest cycle, the harvest valve opens and
allows refrigerant from the top of the receiver tank to
enter the evaporator. The refrigerants change of state
(from vapor to liquid) releases the heat necessary for
the Harvest cycle.
Opening the harvest valve causes a drop in discharge
pressure.
The discharge pressure will drop below the condenser
fan cycling control setpoint and the condenser fan
motor cycles off (at ambient temperatures above
110°F (43°C) the condenser fan motor remains
energized).
The warm discharge gas adds heat to the receiver in
the harvest cycle. Without this additional heat the head
pressure would continue to drop as liquid refrigerant
boils off in the receiver.
Example: A service technician removes refrigerant
vapor from a cylinder by boiling off the liquid
refrigerant. A refrigeration effect is created as the
refrigerant changes state from a liquid to a vapor. The
cylinder cools and the refrigerant pressure drops. To
maximize flow and maintain pressure the technician
places the cylinder in warm water.
A head pressure control valve that will not completely
bypass in the harvest cycle will result in longer harvest
cycles with lower that normal suction pressure and
safety limit #2 trips.
(Refer to the “Cycle Times/24 Hr Ice Production/
Refrigerant Pressure Charts” for the model being
worked on, to obtain the correct harvest cycle
pressure range).
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