This work was a joint development project between Chrysler Corporation and CFD Research Corporation (CFDRC). The objective of this investigation was to perform a 3D flow and heat transfer simulation of a vehicle hot room test. One of the major tasks was to simulate the transient temperature variation in the passenger compartment after the AC unit of the test vehicle is turned on.A fully coupled flow and heat transfer analysis becomes very expensive and time-consuming when radiation is taken into account. This is due to the fact that the interior of a passenger compartment is very complicated in general. A flux tracing method was proposed and implemented to take care of the external radiative heat flux applied on the vehicle in the hot room. This method provides reasonable prediction with a very quick computational turnaround.This study demonstrates that Computational Fluid Dynamics (CFD) technology can be used as a design and prototyping tool for automotive climate control systems.