During cabin warm-up, effective air distribution by vehicle climate control systems plays a vital role. For adequate visibility to the driver, major portion of the air is required to be delivered through the defrost center ducts to clear the windshield. Which results in thermal interaction between warm air delivered from the HVAC unit and the cold windshield. This creates thermal losses since the windshield acts as a heat sink, which delays the heating of passenger compartment causing delay in time to providing thermal comfort to the passenger. Thus it becomes essential to predict the effect of different windscreen defrost characteristics and its impact on occupant thermal comfort. In this paper, sensitivity analysis is carried for different windscreen defrosts characteristics like ambient conditions modes of operation; change in material properties along with occupant thermal comfort is predicted. An integrated 1D/3D CFD approach is proposed to evaluate the same. Detailed thermal boundary conditions are considered in 1D heat transfer method and coupled with 3D convection human comfort model.