This study presents a method for a cool down simulation of passenger compartments. The purpose was to integrate the 3D Computational Fluid Dynamics (CFD) software StarCCM+ with the 1D thermal management software KULI. The targets were to achieve accurate prediction of temperature diffusion inside the cabin for a transient cycle simultaneously reducing the modelling effort and CPU-time consumption. The 1D simulation model was developed in KULI and the flow field data required to simulate mass flow and diffusion inside the cabin was implemented from Star CCM+. The simulation model consists of a multi-zone cabin and models the complete refrigerant circuit consisting of evaporator, condenser, Thermal Expansion Valve (TXV) and compressor. This paper describes the process flow, definition of the inputs required and finally the validation of the simulation data with experiments. Alongwith the temperature profiles, the system pressures of the refrigerant circuit such as the suction pressure and discharge pressure are also validated. The KULI simulation model predicts cabin temperatures within an error of 5 percent and pressures within an error of 10% with a significant reduction in modelling effort and CPU-time consumption as compared with the full 3D CFD simulation.