TPI 750A HVAC Refrigerant Leak Detector is a highly accurate refrigerant leak detector with an impressive 0.2 ounce per year sensitivity. The TPI 750A features detection of existing refrigerants and blends such as 404A, PURON, R-507 (AZ50), one-hand operable thumb-wheel, and a 400 hour life-span sensor with a spare sensor included.