Switch/Relief Valve
Switch/relief valve has a dual function. On cold start, manifold vacuum signal is sent to switch/relief valve and air supply is directed to exhaust manifold. After engine is warm, air supply is directed downstream to catalytic converter. At high speeds, vacuum solenoid cancels vacuum signal to switch/relief valve. Valve is regulated by manifold vacuum and a vacuum solenoid. When vacuum signal to switch/relief valve is canceled, most air supply is diverted to atmosphere. See Fig 1 .