Headmaster Control Valve - Manitowoc S Service Manual

Section 7

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.
Symptom
Valve not maintaining pressures
Discharge pressure extremely high;
Liquid line entering receiver feels hot
Discharge pressure low; Liquid line
entering receiver feels extremely cold
Discharge pressure low; Liquid line
entering receiver feels warm to hot
Ice machine has safety limit #1 on cold
mornings.
Part Number 80-1480-3
Diagnosing
1. Determine the air temperature entering the remote
2. Determine if the head pressure is high or low in
3. Determine the temperature of the liquid line entering
4. Using the information gathered, refer to the chart
NOTE: A headmaster that will not bypass, will function
properly with condenser air temperatures of
approximately 70°F (21.1°C) or above. When the
temperature drops below 70°F (21.1°C), the headmaster
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.
Probable Cause
Non-approved valve
Valve stuck in bypass
Valve not bypassing
Ice machine low on charge
condenser.
relationship to the outside temperature. (Refer to the
proper "Operational Pressure Chart" later in this
section.)
the receiver by feeling it. This line is normally warm;
"body temperature."
below.
Corrective Measure
Install a Manitowoc Headmaster control
valve with proper setting
Replace valve
Replace valve
Locate and repair refrigerant leak.
Refrigeration System
7-27