Motor vehicle air management system

In a motor vehicle having a passenger compartment with an air inlet at the base of a windshield in a positive pressure area on the vehicle and an air outlet at a negative pressure area on the vehicle wherein there occurs a pressure differential during vehicle movement that forces ambient air to flow into the inlet through the passenger compartment and out the outlet and that can also force air to flow into the compartment through a leakage path on the vehicle, the improvement comprising said outlet being located at the most negative pressure area on the vehicle, valve means for varying the area of said outlet, and pressure responsive control means responsive to the pressure in said compartment for controlling said valve means so as to maintain the pressure in said compartment above ambient pressure to prevent entry of ambient air into said compartment through said leakage path.