In this paper, simulation studies of a one TR window air conditioner were carried out with three different mixtures of R22 and R290 M1 (50-50) %, M2 (25-75) % and M3 (75-25) %. Performance parameters like refrigerant mass flow rate, refrigerant capacity, compressor power, C.O.P, condenser inlet temperature, condenser outlet temperature, capillary tube inlet temperature and compressor shell inlet temperature were analyzed at varying conditions, evaporator temperature varied from 60C to120C and condenser temperature varied from 400C to 550C and results were analyzed. Performance parameters of R22 and R290 are compared using CYCLE _D software. Simulation results show that R290 has a maximum mass flow rate. Only a marginal variation of capacity is observed with all working fluids. The condenser inlet temperature is minimum for R290 and maximum for R22. Condenser outlet temperature variation is marginal for all refrigerants. R290 has a minimum power consumption and maximum C.O.P. The simulation results show that the use of hydrocarbon refrigerant (R290) improves the performance of window air conditioner.