In this work, the performance of R134a based automobile air conditioning system has been evaluated by retrofitted with R290/R600a mixture (in the ratio of 50:50, by mass), as an alternative. The performance was evaluated at five different operating speeds (1000, 1500, 2000, 2500, and 3000, which covers the entire range of working conditions) with four different cabin load (100, 200, 300, and 400 W). The condenser inlet air temperature was varied in the range between 30 and 50 °C, which covers the entire climatic variations in Coimbatore city of India. The performance characteristics such as, refrigerating effect, coefficient of performance, compressor power consumption, and compressor discharge temperatures were considered for comparison. The results showed that, hydrocarbon mixture has faster cooling rate due to its high latent heat of vaporization, 5% higher coefficient of performance due to higher refrigeration effect, 8-10 K lower compressor discharge temperature due to its lower specific heat ratio with 5% lower compressor power consumption due to its lower viscosity and lower liquid density. The charge requirement of R290/R600a mixture is about 50% less com-pared to R134a. However, the mixture composition is considered as an interment replacement in automobile air conditioners due to composition shift under leak-age conditions. Hence, R290/R600a mixture is considered as an interim energy efficient and environment friendly option in R134a automobile air conditioners to extend its life.