Adequate visibility through the automobile windshield is of paramount practical significance, most often at very low temperatures when ice tends to form on the windshield screen. But the numerical simulation of the defrost process is a challenging task because phase change is involved. In this study numerical solution was computed by a finite volume computational fluid dynamics (CFD) program and experimental investigations were performed to validate the numerical results. It was found that the airflow produced by the defrost nozzle is highly nonuniform in nature and does not cover the whole windshield area. The nonuniformity also severely affected the heating temperature pattern on the windshield. The windshield temperature reached a maximum in the vicinity of the defroster nozzle in the lower part of the windshield and ranged from 9~$31^{circ}C$ over a period of 30 min, which caused the frost to melt on the windshield. The melting time was under 10 minutes, which satisfied the NHTSA standard. The numerical predictions were in close agreement with the experimental results. Thus, CFD can be a very useful design tool for an automobile HVAC system.