What does low superheat and high subcooling mean?

Low superheat and high subcooling typically indicate that the refrigerant in the system is overcharged.

In a properly functioning HVAC system, superheat refers to the temperature of the vapor refrigerant above its boiling point, which helps determine if the evaporator is working efficiently and if the refrigerant has fully evaporated before returning to the compressor. A low superheat indicates that the refrigerant is not absorbing as much heat as it should and is possibly in liquid form when it enters the compressor, which can lead to compressor damage.

High subcooling, on the other hand, refers to the temperature of the liquid refrigerant below its condensing temperature. When subcooling is high, it suggests that there is an adequate amount of liquid refrigerant in the condenser. However, when combined with low superheat, it signifies that too much refrigerant is present in the system, leading to the conclusion of overcharging.

Therefore, having both low superheat and high subcooling is a strong indication that the system is overcharged with refrigerant.