This paper describes the development of an analytical tool for the design automation of the temperature blend door mechanism in an automotive HVAC system. The function of the blend door is to control the temperature of the air blown into the cabin interior by regulating the mix of air passing through the heater core. The objective in the design process is to achieve a prescribed function of temperature with respect to control position at the instrument panel. The control effort to effect the desired temperature change is also another important consideration for customer satisfaction.The current design process is empirical in nature and relies on laboratory and vehicle testing with prototypes. The process is also iterative in nature and may continue until the end of the overall design cycle of the complete air handling subsystem.A parametric feature-based computer model, described subsequently in detail, allows for virtual prototyping of the blend door control mechanism. With this model, various blend door designs can be explored early in the design cycle. Late changes required for packaging can also quickly be analyzed. Kinematic analysis of the blend door mechanism allows the control curve and control effort to be predictive. This desktop simulation tool will enable designs to be optimized or permit the number of options to be narrowed, which will reduce test time and shorten design cycle time.Illustration of the desktop tool is based upon predicting control curves and efforts for a production HVAC system. Also, airflow and temperature data from CFD analysis for this production system is presented. Finally, predicted results are compared and correlated with actual laboratory and vehicle test data.