A decrease in superheat causes a thermostatic expansion valve to?

A decrease in superheat causes a thermostatic expansion valve to close. This is because the superheat is a measure of how much the refrigerant vapor has been heated above its saturation temperature after it has completely evaporated in the evaporator.

When superheat decreases, it indicates that the refrigerant is not being heated sufficiently, which suggests that excess refrigerant is entering the evaporator. The thermostatic expansion valve uses a sensing bulb that measures the superheat. If the superheat is lower than the desired level, this triggers the valve to reduce the flow of refrigerant into the evaporator. Closing the valve ensures that the system does not flood with too much refrigerant, helping to maintain proper system operation and efficiency.

In summary, the function of the thermostatic expansion valve is to modulate the flow of refrigerant based on the temperature and pressure conditions within the system, protecting it from operational issues associated with overfeeding or underfeeding of refrigerant.