AIR Diverter Valve
WARNING: This page does not describe the selected car, but rather 32 other vehicles, including the 2005 Mercury Sable, 2005 Mercury Mountaineer, 2005 Mercury Monterey, 2005 Mercury Montego, and 2005 Mercury Mariner. However, it is still accessible from the selected car via links, so may be relevant.
The secondary AIR diverter valve is used with the electric AIR pump to provide on/off control of air to the exhaust manifold and catalytic converter. When the electric AIR pump is on and vacuum is supplied to the AIR diverter valve, air passes the integral check valve disk. When the electric AIR pump is off, and vacuum is removed from the AIR diverter valve, the integral check valve disk is held on the seat and stops air from being drawn into the exhaust system and prevents the back flow of the exhaust into the secondary AIR system.