The present study describes the design optimization of blower scroll of an automotive AC system to improve the overall performance. An automobile AC unit mainly consists of blower unit and heating/cooling unit, the blower being very crucial unit controls the basic performance of AC unit such as wind volume, sound and cooling performance. It has always been a general practice to develop HVAC with less sound, a compact design to package easily in the instrument panel and less power/fuel consumption. It is therefore necessary to design and optimize the HVAC unit and blower unit in order to enhance the air flow amount, to increase the flow uniformity on the heat exchanger and duct outlet, to increase the cooling performance, temperature linearity and to reduce the power consumption by the blower motor. A 3-dimensional Computational Fluid Dynamics (CFD) was used to determine the flow characteristics numerically and the simulation results were helped to optimize the base design of HVAC and blower. The results from the numerical prediction are in good agreement with the prototype tested. Thus it has help to reduce the cost and time required to reach the desired objective and to understand many complex situations which will be databank for future program of the HVAC development.