What device controls a thermal electric (solid-state) expansion valve?

The correct choice is a NTC thermistor, which plays a critical role in controlling a thermal electric (solid-state) expansion valve. An NTC (Negative Temperature Coefficient) thermistor is a type of temperature sensor that decreases its resistance as temperature increases. In the context of HVAC systems, this characteristic allows the thermistor to accurately monitor temperature changes in the refrigerant or surrounding environment.

When the thermistor senses changes in temperature, it provides corresponding signals to the electronic control system that adjusts the position of the expansion valve. This precise control helps optimize the flow of refrigerant based on the cooling load, enhancing the overall efficiency of the air conditioning system. This responsiveness to temperature changes is essential for maintaining the desired cooling performance while ensuring energy efficiency.

Other options may involve temperature measurement or system control, but they do not specifically encompass the behavior of the thermistor in relation to the solid-state control of the expansion valve.