Section 7Refrigeration System7-28Headmaster Control ValveManitowoc remote systems require headmastercontrol valves with special settings. Replace defectiveheadmaster control valves only with “original”Manitowoc replacement parts.OPERATIONThe R404A headmaster control valve has a non-adjustable setting of 225 PSIG.At ambient temperatures of approximately 70°F(21.1°C) or above, refrigerant flows through the valvefrom the condenser to the receiver inlet. Attemperatures below this (or at higher temperatures ifit is raining), the head pressure control dome’snitrogen charge closes the condenser port and opensthe bypass port from the compressor discharge line.In this modulating mode, the valve maintainsminimum head pressure by building up liquid in thecondenser and bypassing discharge gas directly to thereceiver.DIAGNOSING1. Determine the air temperature entering the remotecondenser.2. Determine if the head pressure is high or low inrelationship to the outside temperature. (Refer tothe proper “Operational Pressure Chart” later inthis section.) If the air temperature is below 70°F(21.1°C), the head pressure should be modulatingabout 225 PSIG.3. Determine the temperature of the liquid lineentering the receiver by feeling it. This line isnormally warm; “body temperature.”4. Using the information gathered, refer to the chartbelow.NOTE: A headmaster that will not bypass, willfunction properly with condenser air temperatures ofapproximately 70°F (21.1°C) or above. When thetemperature drops below 70°F (21.1°C), theheadmaster fails to bypass and the ice machinemalfunctions. Lower ambient conditions can besimulated by rinsing the condenser with cool waterduring the freeze cycle.Symptom Probable Cause Corrective MeasureValve not maintaining pressures Non-approved valve Install a Manitowoc Headmastercontrol valve with proper settingDischarge pressure extremely high;Liquid line entering receiver feels hotValve stuck in bypass Replace valveDischarge pressure low; Liquid lineentering receiver feels extremely coldValve not bypassing Replace valveDischarge pressure low; Liquid lineentering receiver feels warm to hotIce machine low onchargeSee “Low on Charge Verification” onnext page
