Subcooling is the difference between the saturation temperature at the condensing pressure and the actual temperature of the liquid refrigerant.
Why it is useful
It indicates whether the refrigerant has fully condensed before reaching the expansion valve.
Low subcooling
It may be associated with an insufficient amount of refrigerant or incomplete condensation.
High subcooling
It may be related to overcharging or liquid accumulation in the condenser, depending on the system.