TXVs control a set amount of evaporator superheat to maintain an active evaporator. By controlling evaporator superheat, refrigeration and air conditioning systems can operate safer and more efficiently. This month’s article will cover the causes and effects of a TXV overfeeding refrigerant, while next month’s article will discuss what happens if a TXV valve underfeeds — or starves — the evaporator.

The main function of the TXV is to meter the right amount of refrigerant into the evaporator coil under all evaporator heat loading conditions to maintain a set evaporator superheat. The TXV can do this as long as the pressure and temperature ranges of the valve have not been exceeded (always consult with the valve manufacturer’s literature for detailed information on the pressure and temperature operating ranges of any TXV, as well as operating capacities of each valve).