Refrigerant Testers:

                     Even with the precautions of unique fittings and mandatory on-vehicle lables, A/C service providers still risk costly contamination if a mixture of refrigerants has been introduced into a vehicle's A/C system before it gets to them. For that reason, many are routinely using SAE-approved refrigerant identifiers--devices that "sniff" and identify specific refrigerants. If it cannot determine the exact type, it will indicate that the system contains an unidentified refrigerant or mixture of refrigerants.