Abstract: An applicator for introducing an air conditioning system treatment into an air conditioning system refrigerant flow path. The applicator comprises a reservoir carrying the treatment, the reservoir having first and second caps closing first and second reservoir openings, each of the first and second caps including a hose fitting. First and second hoses are connected between respective first and second valves in the refrigerant flow path and the respective first and the second fittings. A pressure differential between the first and the second valves (a higher pressure at the first valve than at the second valve) forces the treatment from the reservoir through the second hose into the second valve in the refrigerant flow path.