In order to ensure a comfortable space inside the cabin, it is very essential to design an efficient heating ventilating and air-conditioning (HVAC) system which can deliver uniform temperature distribution at the exit. There are several factors which impact on uniformity of temperature distribution. Airflow distribution is one of the key parameter in deciding the effectiveness of temperature distribution. Kinematics links and linkage system typically termed as ‘mechanism’ is one of the critical sub-systems which greatly affects the airflow distribution. It is not the temperature uniformity but also the HVAC temperature linearity also depends on airflow distribution. Hence the design of mechanism is incomparably of paramount importance to achieve the desired level of airflow distribution at HVAC exit.The present paper describes the design methodology of automotive HVAC mechanism system. To this context various parameters which contribute in designing the mechanism were studied and then a layout was made in CAD. Further the design was evaluated numerically using the MBD (multibody dynamics) of Hypermesh software from which torque to drive the mechanism was predicted as well the reaction force at doors. The design was fine tuned to reduce the operating effort. Finally the predicted operating effort was validated by making the physical sample and it is found that numerical results are in good agreement with that of experimental results. So adoption of such methodology in the early stage of design ensures better and better design of automotive HVAC system.