What Is a Thermostatic Expansion Valve (TXV)?

A thermostatic expansion valve is the metering device that controls how much refrigerant enters the evaporator coil, modulating flow in response to how much the refrigerant has superheated. It keeps the coil properly fed across changing conditions instead of at one fixed rate.

Also called: TXV · expansion valve · metering device

Why it matters to you

A correctly operating TXV is part of why a system can hold performance through a hot, humid afternoon rather than only at its rated design point. A failing valve shows up as poor cooling, frost on the lines, or wide swings in performance across the day.

What to do about it

TXV symptoms overlap with low charge and airflow problems, so diagnosis depends on measured superheat and subcooling rather than guesswork. This is licensed refrigerant work.