What does the sensor bulb of a thermostatic expansion valve primarily control?

The sensor bulb of a thermostatic expansion valve plays a crucial role in the refrigeration cycle by primarily regulating the flow of refrigerant into the evaporator. It detects the temperature of the refrigerant vapor exiting the evaporator and adjusts the valve accordingly. When the temperature is low, indicating that the evaporator is working efficiently, the valve opens to allow more refrigerant to flow. Conversely, if the temperature is high, the valve restricts the refrigerant flow to prevent excessive pressure build-up, maintaining optimal evaporator pressure levels.

By controlling the evaporator pressure, the sensor bulb ensures that the evaporator operates within its designed parameters, enhancing efficiency and preventing issues such as liquid floodback to the compressor. This regulatory function is central to the overall performance of the refrigeration system, thereby underscoring the importance of the sensor bulb's role in managing evaporator pressure.