Air Control Valve
Air control valve reacts to vacuum levels (which indicate engine loads) to direct air pump air either into injection manifold or back to the inlet side of air pump. On Auto. Trans. vehicles, air control valve contains one relief valve. Man. Trans. vehicles have an air control valve with two relief valves. One relief valve is closed at low speeds to direct normal air flow into exhaust system. At high speeds it opens to return air flow to the air pump. The second relief valve modulates amount of air reaching exhaust system according to engine loads.