Passenger comfort and safety are major drivers in a typical automotive design and optimization cycle. Addressing thermal comfort requirements and the thermal management of the passenger cabin within a car, which involves accurate prediction of the temperature of the cabin interior space and the various aggregates that are present in a cabin, has become an area of active research. Traditionally, these have been done using experiments or detailed three-dimensional Computational Fluid Dynamics (CFD) analysis, which are both expensive and time-consuming. To alleviate this, recent approaches have been to use one-dimensional system-level simulation techniques with a goal to shorten the design cycle time and reduce costs.This paper describes the use of Modelica language to develop a one-dimensional mathematical model using Modelica language for automotive cabin thermal assessment when the car is subjected to solar heat loading. The developed model has the capability to predict the thermal response of a car cabin and its internal aggregates, such as seats, dashboards, roof, etc. for hot day solar loading conditions. A solar radiation model is established to capture the solar radiation that included movement of the sun position with time. In addition, the model included natural convection heat transfer and solid conduction effects for precise prediction of cabin aggregates temperature.The developed one-dimensional model is validated by comparing its predictions against the prediction of a high-resolution three-dimensional CFD model for a range of boundary and operating conditions. The results show an excellent agreement with CFD results with the temperatures being predicted to within ±2 K of that predicted by the CFD model.