Refrigeration System | Section 7 |
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HEADMASTER CONTROL VALVE
Function
The headmaster control valve maintains the correct discharge pressure and liquid line temperature.
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
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 (21.1°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.
Air-Cooled Condensing Units
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.
3.Determine the temperature of the liquid line entering the receiver by feeling it. This line is normally warm; “body temperature.”
4.Using the information gathered, refer to the chart below.
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. Rinsing the condenser with cool water during the freeze cycle will simulate lower ambient conditions.
Freeze Cycle Headmaster Control Valve Failure List
Symptom | Probable | Corrective | |
Cause | Measure | ||
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Valve not | Install a Manitowoc | ||
maintaining | valve | Headmaster control | |
pressures |
| valve with proper | |
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| setting | |
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Discharge pressure | Valve stuck in | Replace valve | |
extremely high; | bypass |
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Liquid line entering |
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receiver feels hot |
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Discharge pressure | Valve not | Replace valve | |
low; Liquid line | bypassing |
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entering receiver |
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feels extremely cold |
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Discharge pressure | Ice machine | Locate and repair | |
low; Liquid line | low on charge | refrigerant leak | |
entering receiver |
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feels hot |
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| Revised 8/2003 | Part No. |
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