Manitowoc QC0700, Technician'S Handbook

Page: 193 / 292

Part Number 80-1230-9 10/10 193
Headmaster Control Valve
SF900A/SN950A/SF1200A/SN1250A/SF2000A/
SN2050A Remote Condensers, Remote
Condensing Units &
FUNCTION
The headmaster control valve maintains the correct
discharge pressure and liquid line temperature.
These machines use the headmaster at low ambient
conditions to maintain the head pressure and
evaporator suction pressure in the correct range.
Diagnostics are the same for all applications.
Manitowoc Ice Machine systems require headmaster
control valves with special settings. Replace defective
headmaster control valves only with “original”
Manitowoc replacement parts.
FREEZE CYCLE OPERATION
Air-Cooled Ice Machines
During low ambient conditions, it is normal for the
head pressure control valve to hunt (head pressure
may fluctuate up and down) and generally settles out
within the first 6 minutes of the freeze cycle.
At ambient temperatures of approximately 70°F (21°C)
or above, refrigerant flows through the condenser to
the receiver inlet. At temperatures below this (or at
higher temperatures if it is raining), the head pressure
controls nitrogen dome charge starts to modulate
(closes the condenser port and opens the bypass port
from the compressor discharge line).
In this modulating mode, the valve maintains minimum
head pressure by building up liquid in the condenser
and bypassing discharge gas directly to the liquid line.
Freeze Cycle
1. Determine the air temperature entering the
condenser.
2. Determine if the head pressure is high or low in
relationship to the outside temperature. (Refer to
the proper “Operational Pressure Chart”) If the air
temperature is below 70°F (21.1°C), the head
pressure control will modulate to maintain the
correct liquid line temperature and head pressure.