Superheat is the difference between the actual temperature of the refrigerant vapor and the saturation temperature corresponding to the evaporation pressure.
Why it is measured
It indicates whether the refrigerant has fully evaporated before reaching the compressor.
High superheat
It may be related to insufficient refrigerant supply or a restriction in the expansion device.
Low superheat
It may indicate evaporator overfeeding and an increased risk of liquid return to the compressor.