The thermostatic expansion valve (TEV or TXV) is erroneously considered by some to be a mysterious and complex device. As a result, many valves are needlessly replaced when the cause of the system malfunction is not immediately recognized.
Actually the TEV performs only one very simple function - it keeps the evaporator supplied with enough refrigerant to satisfy all load conditions. It is not a temperature control, suction pressure control, a control to vary the compressor's running time, or a humidity control.