A Thermostatic Expansion Valve (TXV, also TEV) is a refrigerant metering device that precisely controls the flow of refrigerant into the evaporator coil based on actual operating conditions. It replaces simpler fixed-orifice metering devices (piston or orifice tube) in higher-efficiency systems.
The TXV senses the temperature and pressure at the evaporator outlet (via a sensing bulb and equalizer line) and continuously adjusts refrigerant flow to maintain proper superheat — ensuring the refrigerant fully evaporates before reaching the compressor.
TXV systems are more efficient than fixed-orifice systems because they adapt to varying load conditions rather than operating at a fixed flow rate. They require more precise refrigerant charge and are more sensitive to installation quality. TXVs are standard in SEER2 13.4+ equipment and are required for proper system matching with many modern condensing units.