Heat management must allow the adjustment of optimal operating temperatures of all components of a vehicle. A comprehensive simulation model (KULI) will contain all components relevant for heat management. This includes heat sources, heat exchangers, fans, etc. Main aspects of the simulation are flow and heat transfer analysis. Not only the engine cooling system can be covered with this simulation tool, also the air-conditioning circuit including phase changing models is a part of it (KULI AC). To fulfill the needs of integrating various software tools to an overall simulation cluster an interface to a fluid flow 1-dimensional software (FLOWMASTER) was developed. The use of 1- dimensional methods and mesh flow theory for modeling the underhood air flow of vehicles is very efficient method. For complex flow patterns however it is desirable to use CFD analysis. To serve this demand a procedure was developed to include data of CFD analysis (STAR-CD) into the 1-dimensional simulation model. Three applications that show the various software integration and interface facilities will be presented.