The level of infotainment in today's vehicles and the customer expectation of the functionality imply a significant effort is required on thermal management of the systems, to guarantee their full operation under all operating conditions. The worst case thermal conditions the system will get exposed to are caused by solar loading on the cabin or heat up as a result of cabin heating.Simulation of a solar load driven case will be discussed in this paper. The long soak conditions during these tests result in the modelling requirement for long natural convection periods. This is creating a challenge for the conventional CFD simulations in turnaround time. New simulation methodology has resulted in significant speed up enabling these fully transient simulations in a reasonable turnaround time to enable programme support. A two phase approach to simulating this problem is proposed in this paper.Results for both phases and the comparison against vehicle climatic wind tunnel tests are discussed in the paper. The newly developed methodology will enable early assessment in the programme development of the environmental conditions in the vehicle cabin. This will support the package of infotainment units through better positioning in low ambient areas in the vehicle cabin and reducing the forced cooling requirement.