ICE MACHINES Q-Model Service Manual

Refrigeration System Section 7HEADMASTER CONTROL VALVEManitowoc remote systems require headmaster controlvalves with special settings. Replace defectiveheadmaster control valves only with “original” Manitowocreplacement parts.OperationThe 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 thecondenser to the receiver inlet. At temperatures belowthis (or at higher temperatures if it is raining), the headpressure control dome’s nitrogen charge closes thecondenser port and opens the bypass port from thecompressor discharge line.In this modulating mode, the valve maintains minimumhead pressure by building up liquid in the condenser andbypassing discharge gas directly to the receiver.Diagnosing1. Determine the air temperature entering the remotecondenser.2. Determine if the head pressure is high or low inrelationship to the outside temperature. (Refer to theproper “Operational Pressure Chart” later in thissection.) 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 line enteringthe receiver by feeling it. This line is normally warm;“body temperature.”4. Using the information gathered, refer to the chartbelow.NOTE: A headmaster that will not bypass, will functionproperly with condenser air temperatures ofapproximately 70°F (21.1°C) or above. When thetemperature drops below 70°F (21.1°C), the headmasterfails to bypass and the ice machine malfunctions. Lowerambient conditions can be simulated by rinsing thecondenser with cool water during the freeze cycle.Symptom Probable Cause Corrective MeasureValve not maintaining pressures Non-approved valve Install a Manitowoc Headmaster controlvalve with proper settingDischarge pressure extremely high; Valve stuck in bypassReplace valveLiquid line entering receiver feels hotDischarge pressure low; Liquid lineentering receiver feels extremely coldValve not bypassingReplace valveDischarge pressure low; Liquid lineentering receiver feels warm to hotIce machine low on chargeSee “Low on Charge Verification” onPage 7-317-30 Part No. 80-1100-3