An increase in heat (superheat) on the bulb of a TXV causes what effect?

An increase in heat, or superheat, sensed by the bulb of a thermostatic expansion valve (TXV) leads to the valve opening more, or staying open longer. This response occurs because the TXV is designed to regulate the flow of refrigerant based on the temperature and pressure of the refrigerant vapor. The bulb senses the superheating of the refrigerant, indicating that more refrigerant is needed to maintain the correct superheat in the evaporator.

When the temperature at the bulb increases, the expansion of the refrigerant inside the bulb causes the diaphragm in the TXV to move, allowing the valve to open further. This increases the flow of refrigerant into the evaporator, helping to absorb more heat and maintain proper system function. Thus, the increase in superheat directly correlates to a mechanism that allows for more refrigerant flow in order to optimize the system's performance and efficiency.