Manitowoc QD0202A, Service Manual

Page: 140 / 175

Refrigeration System Section 7
7-28
Part No. 80-1100-3
FREEZE CYCLE
The H.P.R. system is not used during the freeze cycle.
The H.P.R. solenoid is closed (de-energized), preventing
refrigerant flow into the H.P.R. valve.
HARVEST CYCLE
During the harvest cycle, the check valve in the
discharge line prevents refrigerant in the remote
condenser and receiver from backfeeding into the
evaporator and condensing to liquid.
The H.P.R. solenoid is opened (energized) during the
harvest cycle, allowing refrigerant gas from the top of the
receiver to flow into the H.P.R. valve. The H.P.R. valve
modulates open and closed, raising the suction pressure
high enough to sustain heat for the harvest cycle,
without allowing refrigerant to condense to liquid in the
evaporator.
In general, harvest cycle suction pressure rises, then
stabilizes in the range of 75-100 psig (517-758 kPA).
Exact pressures vary from model to model. These can
be found in the “Operational Refrigerant Pressures”
charts, beginning on
Page 7-32 .