This paper presents a multiphase simulation of evaporator in automotive air conditioning system was done by using R134a and R1234yf as working fluid (refrigerants) to know the performance parameters. A CFD model was built to simulate the multiphase flow and the Thermal analysis is carried out for the evaporator by using R134a and R1234yf refrigerants with constant mass flow rate. The results obtained after the simulation are expressed in the figures of volumes fraction, temperature, velocity of refrigerants. The CFD simulation was compared with both the refrigerants. And it was also thus conforming that the CFD model was successful in reproducing the heat and mass transfer process in HVAC evaporator using R134a and R1234yf refrigerants. © IAEME Publication.