What Is Superheat and Subcooling?

Superheat and subcooling are the two measurements used to verify refrigerant charge. Superheat is how much the refrigerant vapour has warmed past its boiling point leaving the evaporator; subcooling is how far the liquid has cooled below its condensing point leaving the condenser.

Also called: superheat · subcooling · charge verification

Why it matters to you

These are the numbers that distinguish a properly charged system from one that merely runs. A system can appear to work while being under- or overcharged, slowly damaging the compressor and quietly costing efficiency on every hot afternoon.

What to do about it

Ask whether charge was verified by measurement on any repair involving refrigerant, and which method applies to your metering device — subcooling for a TXV system, superheat for a fixed-orifice one. A technician adding refrigerant without taking readings is guessing.