What happens to the thermostatic expansion valve when there is a decrease in superheat?

When there is a decrease in superheat, the thermostatic expansion valve (TXV) begins to close. This occurs because the TXV is designed to regulate the flow of refrigerant into the evaporator based on the superheat level. Superheat is the amount of heat added to refrigerant vapor above its saturation point.

A decrease in superheat indicates that there is more refrigerant vapor in the evaporator than ideal, suggesting that the evaporator is absorbing less heat from the environment. In response, the TXV will close slightly to reduce the flow of refrigerant into the evaporator. This action helps prevent liquid refrigerant from entering the compressor, which can lead to damage.

It's important for the efficiency and protection of the system that the TXV responds to changes in superheat in this way, allowing the system to adapt to varying cooling loads and maintain optimal performance.