The Fieldpiece Superheat and Subcooling Accessory for Air Conditioning, model ASX14, measures suction line, or low side, line temperature and pressure. It then calculates actual superheat in real time using built in P/T charts. It also measures liquid line, or high side, line temperature and pressure, and calculates actual subcooling. Use it to get actual superheat on R-22 and R-410A fixed orifice systems and actual subcooling on TXV / TEV regulated systems. Use the “T” fitting to charge to actual superheat or subcooling by putting the ASX14 in-line between your refrigerant bottle and the system.