What occurs when there is a decrease in superheat in a thermal expansion valve (TEV)?

A decrease in superheat in a thermal expansion valve (TEV) indicates that the refrigerant is becoming closer to its saturation point. Superheat is the temperature of the refrigerant vapor above its boiling point at a given pressure. When superheat decreases, it signals that there is more refrigerant vapor entering the TEV, meaning it's starting to absorb more heat and can handle more refrigerant than before.

As the superheat levels drop, the TEV responds by allowing more refrigerant to flow into the evaporator coil. This is because the primary function of the TEV is to regulate the flow of refrigerant based on the temperature of the refrigerant vapor as it exits the evaporator. Allowing more refrigerant flow helps to optimize the cooling process, ensuring that the evaporator coil has enough refrigerant to effectively absorb heat and maintain efficient operation.

In contrast, if superheat were to increase, the TEV would begin to close, restricting refrigerant flow to prevent flooding the evaporator and maintain the right balance for optimal cooling. Therefore, a decrease in superheat directly results in the TEV opening to accommodate more refrigerant flow.