Also known as a Condenser Pressure Regulator. This component is used in many different applications is often misdiagnosed. The headmaster controls the head pressure of a refrigeration system during low ambient conditions. This ensure proper pressure drop across the expansion device.
A headmaster is usually seen on a condenser that is located outdoors in climate where the outdoor ambient temperature may get colder than the box temperature. Most headmasters are design to begin operating at around 50°F. Although it is designed to operate at 50°F, this is not a temperature controlled device as explained below.
The headmaster consists of three different ports. One connects to the condenser, one to the receiver, and on directly to the discharge line. Under normal conditions, the pressure from the receiver pushes against the valve dome pressure and keeps the seat closed between the discharge line and receiver. This forces the discharge gas through the condenser coil to release heat and condense as in a normal system. As the condenser pressure drops, the dome pressure forces the seat open and allows a portion of the discharge gas to go directly into the receiver, bypassing the condenser coil. This increases the head pressure. As the head pressure rises, it overcomes the dome pressure stopping the refrigerant flow to the receiver. The valve opens and closes proportionally maintaining the desired head pressure. The headmaster is pre-set at the factory and is not adjustable.
The headmaster can fail in two ways:
1. Stuck in the bypass position: This will cause the head pressure to rise causing long freeze cycles or sometime the unit will trip out on the high head pressure control. The easiest way to determine if the valve is stuck in the bypass position is to feel the line that goes in to the receiver. If it is hot to the touch, the valve is stuck in the bypass condition. Also if the head pressure is higher than the rating of the valve it is probably stuck.
2. Not bypassing: This will cause the head pressure to be lower then the rating of the valve and the line going into the receiver is not hot the valve is not bypassing correctly. NOTE – These are also the symptoms if there is a low charge. Before replacing the headmaster that appears as if it is not bypassing, add a few pounds of refrigerant. If the system is low on charge, the additional refrigerant will raise the head pressure and cause the valve to operate.
By Ron Walker
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