Headmaster Control Valve - Manitowoc Q450 Service Technician's Handbook

Headmaster Control Valve

Manitowoc remote systems require headmaster
control valves with special settings. Replace defective
headmaster control valves only with "original"
Manitowoc replacement parts.
OPERATION
The R404A headmaster control valve is non
adjustable.
At ambient temperatures of approximately 70°F
(21.1°C) or above, refrigerant flows through the valve
from the condenser to the receiver inlet. At
temperatures below this (or at higher temperatures if it
is raining), the head pressure control dome's nitrogen
charge 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 receiver.
DIAGNOSING
1. Determine the air temperature entering the remote
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 should be modulating about 225 PSIG
(1551 kPa).
3. Determine the temperature of the liquid line
entering the receiver by feeling it. This line is
normally warm; "body temperature."
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