What indicates a plugged metering device in an HVAC system?

A plugged metering device in an HVAC system typically results in high suction gas superheat. This condition occurs because the metering device is responsible for controlling the flow of refrigerant into the evaporator coil. When the device becomes blocked or plugged, it restricts the refrigerant flow, leading to insufficient refrigerant reaching the evaporator.

As a consequence, the evaporator cannot absorb heat effectively, which causes the temperature of the refrigerant in the suction line to increase as it exits the evaporator. This rise in temperature leads to high superheat readings. Monitoring superheat levels is vital for diagnosing system performance issues, and high superheat signals that the refrigerant is experiencing excessive heat absorption, which indicates a potential blockage upstream in the metering device.

Other choices refer to different conditions that may indicate other issues within the HVAC system. For instance, low discharge pressure often indicates system underperformance but does not specifically point to a plugged metering device. Low ambient temperature can affect system operation but is not a direct indicator of a metering device problem. High liquid line pressure may also occur, but it is not specific to a plugged metering device; it could indicate other issues or system states. Therefore, high suction gas superheat is the most accurate and