What does the expansion valve control in a refrigeration system?

The expansion valve plays a critical role in a refrigeration system by controlling the pressure and flow of refrigerant into the evaporator. Its primary function is to reduce the pressure of the refrigerant as it exits the condenser, transforming it from a high-pressure liquid to a low-pressure mixture of liquid and vapor. This drop in pressure causes the refrigerant to cool, allowing it to absorb heat effectively from the surrounding environment when it enters the evaporator.

By regulating the flow of refrigerant, the expansion valve ensures that the evaporator operates efficiently, optimizing the system's overall performance. This control mechanism is essential for maintaining the desired temperature within the system and for preventing issues such as flooding or starving the evaporator, which could lead to inefficiencies or damage.

In contrast, the other options do not pertain to the specific function of the expansion valve. For example, controlling the flow of air through the ducts relates to the air distribution system, while the operation of the compressor is governed by its own set of mechanisms separate from the expansion valve. The temperature of the outdoor unit is influenced by various components, but it is not directly managed by the expansion valve. Thus, the key responsibility of the expansion valve is explicitly tied to adjusting how refrigerant enters the evaporator