Which type of expansion valve is described as solid-state and controlled by an NTC parameter?

• A. Thermal-electric expansion valve
• B. Capillary tube
• C. Manual expansion valve
• D. Thermostatic expansion valve

Answer: (A)

Electronic control of refrigerant flow relies on a solid-state sensor to adjust how much refrigerant can enter the evaporator. In a thermal-electric (electronic) expansion valve, an NTC thermistor serves as the temperature sensor. The resistance of an NTC decreases as temperature rises, and the control electronics interpret that change to modulate the valve opening—usually by driving a motor or solenoid—to maintain the desired evaporator conditions and superheat. This setup offers precise, automatic regulation compared with purely mechanical or fixed methods.

The other options don’t fit because they operate without electronic sensing. A capillary tube is just a fixed restriction with no regulation. A manual expansion valve relies on a human adjustment and lacks automatic control. A thermostatic expansion valve uses a refrigerant-filled sensing bulb and a mechanical linkage to control the valve, not a solid-state sensor like an NTC.