Refrigerant-12 which is commonly used in air conditioning is among the substances to be phased out internationally. R-134a, which is a chlorine-free refrigerant, is the industry chosen substitute for R-12. In this study, a car air conditioned by R-12 is selected. The car is fitted with appropriate sensors and gauges to measure the car AC performance. First, the performance is measured when it is running with R-12. Careful retrofitting is then made, including adjustment, changing parts, oil and R-12 to R-134a. The performance of the retro fitted AC with R-134a is then measured. Comparison between the two cases is made for different engine RPMs. The AC system was tested twice to see the effect of ambient temperature on the performance. The results of the comparison are very encouraging with better performance on the side of the R-12 case. The results were also compared with car manufacturer＇s recommended performance checks, and found to be satisfactory.