This paper focuses on factors that enhance energy efficiency of air conditioning system on mid-sized, standard and premium buses with engine power from 125 to 280 HP. It covers aspects like light weighting of roof air conditioning system, usage of optimized ducting system with minimal resistance to blowers, deployment of rotary scroll compressor with fast idle control in place of reciprocating piston compressor. The scope of this paper covers AC compressors driven by main engine of vehicle/ bus, study related to auxiliary/donkey engine driven AC compressor is not considered.Context- In order to enhance fuel efficiency in buses an energy efficient air conditioning system should be deployed. This will lead to reduced parasitic load on the engine and translate into direct fuel saving. The parasitic load mainly consists of power consumed by air conditioning compressor to pump the refrigerant and by blower motors and condenser fans for movement of conditioned air and heat removal respectively.Necessity- Due to improved standard of living, most bus commuters prefer a comfortable mode of transport. Mid-size standard and premium buses which offer energy efficient air conditioning, good thermal comfort at elevated ambient temperatures (45 °C to 48 °C), no dust/pollution, minimum noise and minimal vibration inside the passenger compartment will be a win-win situation for both the commuter and the bus operator.Challenge- In order to provide thermal comfort on mid-size, standard and premium buses, automotive thermal engineer has to strike a balance across multiple requirements such as packaging, fuel economy, drivability and grade ability. Further high heat load of 14 to 30 kW coming from 32 to 45 passengers, larger glass areas, limitation on glass tint percentage, mandate for not using curtains need to be balanced by lightweight and energy efficient air conditioning system.