
138
When the temperature drops below 70°F (21°C), the
head pressure control valve fails to bypass and the ice
machine malfunctions. Lower ambient conditions can
be simulated by rinsing the condenser with cool water
during the freeze cycle.
FAN CYCLE CONTROL VS. HEAD PRESSURE
CONTROL VALVE
A fan cycle control cannot be used in place of a head
pressure control valve. The fan cycle control is not
capable of bypassing the condenser coil and keeping
the liquid line temperature and pressure up.
This is very apparent when it rains or the outside
temperature drops. When it rains or the outside
temperature drops, the fan begins to cycle on and off.
At first, everything appears normal. But, as it continues
raining or getting colder, the fan cycle control can only
turn the fan off. All the refrigerant must continue to flow
through the condenser coil, being cooled by the rain or
low outside temperature.
This causes excessive sub-cooling of the refrigerant.
As a result, the liquid line temperature and pressure
are not maintained for proper operation.
Condition
Probable
Cause
Corrective
Measure
Discharge Pressure - High
Liquid Line Temperature - Hot
Valve stuck
in bypass
Replace
valve
Discharge Pressure - Low
Liquid Line Temperature - Cold
Valve not
bypassing
Replace
valve
Discharge Pressure - Low
Liquid Line Temperature - Hot
Ice
Machine
Low on
Charge
Low on
Charge
Verification
STH13_Tech.book Page 138 Wednesday, September 15, 2010 3:20 PM