Abstract-Environmental awareness and energy efficiency are important concepts in terms of sustainability. Regarding the negative impact on the ozone layer, the largest portion is due to the refrigerants used with a share of 31% caused by mobile air conditioning (MAC) systems. In this study, refrigerants used in MAC systems were discussed in the terms of environmental aspects. First, the cooling capacity of the bus was calculated by using ASHRAE Handbook and EN 14750 -1 standard for the city of Istanbul in Turkey. Next, a conventional MAC system (with R134a) used for a bus was considered and the performance tests of this system were performed at SAFKAR Inc., located in the city of Izmir, Turkey while the calculations for R744 were made using experimental values of R134a at the same capacity. Finally, various aspects were presented.