In the future, refrigeration and air-conditioning professionals will face the following challenges : adapting replacement refrigerants, improving containment, reducing refrigerant fluid charge, achieving better energy efficiency, increasing reliability and reducing costs. So more compact and lighter heat exchangers have been developed and have led to real gains in terms of cost, efficiency and charge. Among compact heat exchangers, we focus in this paper on the minichannel technology (hydraulic diameter < 3mm) that seems able to reduce the total system charge about 30% to 60% compared to conventional exchangers. This paper presents simulation results of refrigerant fluid charge and pressure drop within minichannels evaporators for both refrigerants R134a and CO². Different minichannel evaporators are studied with three usual inner-diameter 0.8, 1.7 and 2.7 mm. The importance of selecting appropriate void fraction and pressure drop correlations is discussed. This study is carried out on an evaporator of typical air conditioning car system with 5 kW refrigerating power at a 5°C saturation temperature.