From the end of 1997, Kyoto Protocol has forced system engineers to look more about their system green house contribution. In this paper, we use Total Equivalent Warming Impact analysis to understand what are the key issues between various A/C systems possible for the future. Estimation of TEWI is done using experimental data but also precise simulation results when available. A/C systems using refrigerant HFC R134a and C02 R744 are taken into account but also system based on electric compressor due to the possible change in automotive engine technology to hybrid and fuel cells. Two major topics are considered: the first one is relative to acceptable leakage of refrigerant and the second one is the control of the A/C system around optimal conditions in respect with the fuel consumption.