Freeze Cycle; Harvest Cycle; Hpr Diagnostics - Manitowoc SD0302A Technician's Handbook

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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 70-100 psig (517-758 kPA).
Exact pressures vary from model to model. Refer to
the "Operational Refrigerant Pressures" charts
page 191.

HPR DIAGNOSTICS

Steps 1 through 4 can be quickly verified without
attaching a manifold gauge set or thermometer.
All questions must have a yes answer to continue
the diagnostic procedure.
1. Liquid line warm?
(Body temperature is normal)
If liquid line is cooler than body temperature, refer
to head pressure control valve diagnostics
page 164.
2. Ice fill pattern normal?
Refer to "Ice Formation Pattern" if ice fill is not
normal page 110.
162
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Part Number 80-1479-3 7/10