Valeo Thermal Systems is developing a software package for the design and simulation of a car air-conditioning systems. This software package aims to improve Valeo's response to customer requirements concerning delays for design and sizing system performance and cost reduction.Further it shall help to capitalise our competece and expertise on the A/C systems. The validation of this software is in progress. The software is made up of two modules: A first module for car cabin thermal simulation in dynamic and stationary regimes. A second module for the determination and optimisation of the components for designing an A/C system. A third module is under development for the dynamic simulation of the A/C system functioning in nonstandard conditions.