Vacuum Switching Valve Assembly No. 1 (ES300)
WARNING: This page is about a different car, the 2002 Lexus RX 300 and 2002 Lexus ES 300. However, it is still accessible from the selected car via links, so may be relevant.
Using an ohmmeter, ensure 33-39 ohms are present between vacuum switching valve assembly No. 1 terminals at 68°F (20°C). Check that air flows from port "B" to filter. Apply battery voltage across terminals. Check that air flows from port "B" to port "A". See Fig 1.