The metering or expansion valve controls what aspect of the refrigerant flow?

The metering or expansion valve is critical for controlling the flow of refrigerant in a refrigeration system. Its primary purpose is to regulate the amount and rate at which refrigerant enters the evaporator. By doing this, the valve ensures that the refrigerant is adequately vaporized, which facilitates effective heat absorption. The control of flow is essential because it directly affects the system’s efficiency and performance.

When the metering valve opens and closes, it adjusts the volume of refrigerant that can pass through, thereby enabling the system to maintain optimal functioning based on varying load conditions. If too much refrigerant flows, it can result in flooding the evaporator, while insufficient flow can lead to poor cooling performance.

The other options incorporate aspects of the refrigerant's properties but do not specifically pertain to the valve's primary function. While the valve can indirectly influence temperature and pressure by controlling how much refrigerant is allowed into the evaporator, the most direct control exerted by the metering or expansion valve is over the flow of refrigerant. This is why flow is the correct focal point when discussing the function of the metering or expansion valve.