Which component is responsible for maintaining evaporator superheat in a chilled refrigerant system?

• A. Condenser fan
• B. Automatic expansion valve
• C. Receiver-drier
• D. Lubrication system

Answer: (B)

Evaporator superheat is kept at a set level by the expansion device that feeds the evaporator. The automatic (thermostatic) expansion valve senses the temperature of the vapor leaving the evaporator and adjusts how much liquid refrigerant enters the evaporator. If the sensed superheat is too low, indicating risk of liquid returning to the compressor, the valve restricts flow. If superheat is too high, it opens more to bring the superheat down. This precise control prevents liquid slugging while ensuring the evaporator gets enough refrigerant vapor.

The other components aren’t responsible for maintaining evaporator superheat: the condenser fan helps reject heat on the high-pressure side, the receiver-drier stores refrigerant and removes moisture, and the lubrication system keeps the compressor lubricated.