A metering device that adjusts refrigerant flow to hold evaporator superheat roughly constant.
A TXV senses suction line temperature through a bulb at the evaporator outlet and evaporator pressure (internally or through an external equalizer). It opens to feed more refrigerant when superheat rises and closes when it falls.
Because the valve holds superheat near its setting over a range of charge levels, superheat says little about the charge on a TXV system. Use subcooling to check the charge. Bulb placement and insulation matter: a loose or uninsulated bulb reads the wrong temperature.
Exam work areas
D · Installing systems and controls E · Commissioning and start-up F · Maintenance, service and troubleshooting