The United States Environmental Protection Agency (EPA) as well as the European Commission (EC) are developing test procedures to regulate mobile air conditioning system (MAC) efficiency to reduce greenhouse gas emissions and reduce global warming. In the United States, air conditioning related MAC credits can be earned by implementing an internal heat exchanger (IHX) into a MAC system. By integrating an IHX into a MAC system the, Coefficient of Performance (COP) can be increased at the same time increasing cooling capacity. This improvement in efficiency reduces the energy and/or fuel consumption of the MAC system.This paper will compare various IHX plumbing configurations for a dual evaporator system with R1234yf refrigerant. A MAC system optimized for efficiency as well as evaporator cooling capacity is used to assess these different IHX plumbing configurations. Factors that will be considered include IHX heat transfer rate, suction pressure drop, and the impact of these factors on the COP and cooling capacity. The optimal IHX plumbing configuration for this dual evaporator system will be identified and its integration into the vehicle discussed. This paper also describes the MAC system, test facility used and the testing procedure applied.