This paper presents a method for a cool down simulation of passenger compartments. Main targets were the reduction of modelling effort, limited CPU-time consumption, high accuracy, allowing the prediction of temperature diffusion in the cabin for parameter studies for transient analysis. The process is based on a 1D model, while 3D effects like diffusion fields and mass flow fields are implemented from CFD data. For a given flow field, the transport of heat and humidity are computed. The simulation model contains a specifically developed multi zone cabin model, which can deal e.g. with multiple inlets into the cabin, solar radiation, and recirculation for pre-defined cabin types. Different materials for the cabin walls, like doors, floor, roof and windows are considered by a multi-layer model. To describe the transient cool down behaviour of the HVAC air-path, the simulation was done with a full AC circuit, consisting of evaporator, condenser, TXV and compressor. The transient thermal behaviour of walls and internal masses is considered. The AC system is combined with a 1D model of the engine cooling package. The simulation of the AC circuit is based on the transient behaviour of the cabin. The presented paper covers the definition and the description of the workflow as well as the verification with test data.