Comfortable journey with commercial buses is an essential goal of transportation companies. An air-conditioning system can play an important role for this comfortable journey but it can put extra load on the engine and extra cost in the fuel consumption. The purpose of this work is to increase the performance of air-conditioning system of the buses by reducing the load on the engine and fuel consumption. Using a two-phase ejector as an expansion valve can increase the coefficient of performance (COP) of the air-conditioning system. An improvement in the COP can reduce the empty vehicle weight and fuel consumption of buses. Two-phase ejector dimensions can be determined using the empirical methods available in the literature. In this paper, the two-phase ejector dimensions of air conditioning system for a bus are calculated using the analytical and numerical methods. First of all, the thermodynamic analysis of the vapor-compression refrigeration cycle with a two-phase ejector is performed, and then the ejector dimensions are subsequently determined. The cooling loads of the midibus and bus with R134a as a refrigerant are assumed to be 14Â kW and 32Â kW, respectively. The total length of the two-phase ejector for the midibuses and buses due to these cooling loads, are computed to be 480.8Â mm and 793.1Â mm, respectively. Also, an experimental setup is installed on a truck air conditioner to turn it into the ejector air conditioning system to validate theoretical results with the experimental study. - Highlights: â€¢ Determination of two-phase ejector dimensions of a bus air-conditioning system. â€¢ Thermodynamic analysis of the two-phase ejector cooling system. â€¢ Experimental study on a midibus air conditioner using two-phase ejector.