Which device controls refrigerant flow into the evaporator?

• A. Capillary tube
• B. Three-way valve
• C. Thermal expansion valve
• D. Auto expansion valve

Answer: (D)

Expansion devices regulate the amount of liquid refrigerant entering the evaporator. The auto expansion valve is designed to automatically adjust its opening in response to evaporator pressure and load, so the evaporator receives the right amount of refrigerant to absorb heat without flooding or starving. A capillary tube is just a fixed restriction and can’t adapt to changing conditions. A three-way valve mainly directs flow between circuits rather than controlling how much goes into the evaporator. A thermal expansion valve also modulates flow, but the auto expansion valve is the one specifically associated with automatic control of flow into the evaporator.