TXV / expansion valve

A TXV (thermostatic expansion valve) — or more generally an expansion/metering valve — is the device that meters liquid refrigerant into the evaporator coil at exactly the right rate, and it's the dividing line between the system's high-pressure and low-pressure sides. Its job is to hold the correct superheat: it senses how much the refrigerant is heating in the evaporator and opens or closes to feed more or less, adapting as the cooling load changes. Get it right and the coil is fully and efficiently used; a stuck, failed or wrongly-set TXV causes classic faults — starving the coil (poor cooling, high superheat, icing) or overfeeding it (liquid floodback toward the compressor). You'll find expansion valves in split ACs and, just as importantly, in commercial refrigeration — fridges, freezers and walk-in cold rooms — so a cold room or fridge that won't hold temperature can be a TXV problem. Diagnosing and replacing one is refrigeration-tech work; for commercial kitchen units it's a kitchen-equipment/refrigeration specialist's job.