A low refrigerant charge with an automatic expansion valve used as a metering device will result in?

A low refrigerant charge when using an automatic expansion valve as a metering device will indeed result in high superheat. This occurs because the valve is designed to maintain a specific flow of refrigerant to the evaporator based on the pressure sensing mechanism. With a low refrigerant charge, the pressure within the evaporator decreases, leading to insufficient refrigerant flow. As a result, the refrigerant may not fully evaporate as it absorbs heat, causing the temperature of the refrigerant gas upon exiting the evaporator coil to rise significantly above the saturation temperature. This increase in temperature measures as high superheat, indicating that the refrigerant is in a gaseous state and is effectively capturing heat but is not performing optimally due to the inadequate refrigerant level.

In this context, normal and low superheat would not apply since the low refrigerant charge disrupts the intended functioning of the evaporator. Increased cooling efficiency is also not a result of a low refrigerant charge; in fact, the overall system efficiency would suffer due to poor heat exchange and inadequate cooling capacity. Therefore, high superheat is the correct outcome in this scenario.