Manitowoc Q450 Service Technician's Handbook page 119

• Harvest pressure regulating valve (H.P.R. valve).
This is a pressure regulating valve which modulates
open and closed, based on the refrigerant pressure
at the outlet of the valve. The valve closes
completely and stops refrigerant flow when the
pressure at the outlet rises above the valve setting.
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. Refer to
the "Operational Refrigerant Pressures" charts.
OUTLET
HPR VALVE
–109–
INLET
SV3053