Superheat and subcooling

Headnote

HELPING YOU PREPARE FOR A FUTURE IN HVACR HELPING YOU PREPARE

As refrigerant courses through your typical residential air conditioning system (one consisting of a direct expansion evaporator coil and an air-to-air condenser), its state changes from a vapor to a liquid and then back to a vapor. For the system to produce years of proper cooling, it is imperative that the refrigerant be in the right state at the right time in the right location. As we cannot see inside of the system piping and components, how can we tell just what state the refrigerant is in? By taking superheat and subcooling measurements.

SUPERHEAT

Superheat is the amount of heat added to a dry vapor, in the absence of liquid, to raise the vapor temperature above its boiling point (saturation point) corresponding to the pressure at which it is operating. If there is liquid refrigerant present, there can be no superheat.

Refrigerant enters the evaporator in...