:The air conditioning systems of a fleet of sixteen (16) globally distributed vehicles have been retrofit to HFC-134a and ester-based lubricants. The variables of a generic flush-type retrofit procedure have been systematically changed. The effects of compressor condition (new or pre-conditioned), desiccant type (re-used XH-5 or new XH-7), evacuation times, and charge of mineral oil and HFC-134a were examined, in an attempt to better understand the significance of these specific variables on performance and durability of mobile air conditioning systems under retrofit conditions. Initial performance, measured qualitatively by cooling performance and quantitatively by compressor clutch cycling, is judged to be acceptable. Additional information will be provided, as available, on long-term durability of these systems.