Which of the following is a refrigerant capacity control used with the thermal expansion device?

• A. Capillary tubes
• B. Electronic expansion valve
• C. Piston valves
• D. Condenser coil

Answer: (A)

Capillary tubes provide a simple, fixed restriction that throttles refrigerant as it moves into the evaporator, creating a controlled, limited flow. The amount that can enter the evaporator is determined by the pressure difference across the tiny bore and the tube’s dimensions, giving a built-in capacity control that matches system load when paired with the thermal expansion device. This passive, no-moving-parts approach is why capillary tubes are described as a refrigerant capacity control used with the expansion device. In contrast, an electronic expansion valve actively modulates flow based on sensors, a piston valve is a different type of valve not typically described as a capacity control in this context, and a condenser coil is part of the heat rejection side and not a metering/control device for the evaporator.