The heated air intake was used on many 1970s vehicles to reduce startup emissions on carbureted engines. The systems typically used a thermostat that would open a vacuum switch. The vacuum would act on a diaphragm of a vacuum pot that would pull shut a door to divert the intake air. This would pull air from a chamber that surrounded the exhaust manifold. These devices helped to heat the air entering the carburetor so there was better fuel atomization. Most of the systems failed when the tube connecting the air cleaner and exhaust manifold became dislodged. The other major problem was the rust shield on the exhaust manifold rusting away over time.