Koolaire STH045 8/15 Technician's Handbook page 101

FREEZE CYCLE
The HPR system is not used during the freeze cycle.
The HPR solenoid is closed (de-energized),
preventing refrigerant flow into the HPR valve.
HARVEST CYCLE
During the harvest cycle, the check valve in the
discharge line prevents refrigerant in the remote
condenser and receiver from back feeding into the
evaporator and condensing to liquid.
The HPR solenoid is opened (energized) during the
harvest cycle, allowing refrigerant gas from the top of
the receiver to flow into the HPR valve. The HPR 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
stabilize. Exact pressures vary from model to model.
Refer to cycle time/24 hour ice production and
operational pressure charts.
HPR DIAGNOSTICS
Steps 1 through 5 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.
2. Ice fill pattern normal? 
Refer to "Ice Formation Pattern" if ice fill is not
normal.
3. Freeze time normal? 
(Refer to Cycle Times/Refrigerant Pressures/24
Hour Ice Production Charts).
Shorter freeze cycles - Refer to head pressure
control valve diagnostics.
Longer freeze cycles - Refer to water system
checklist, then refer to Refrigeration Diagnostic
Procedures.
Part Number STH045 8/15 101