Airflow Selector
WARNING: This page is about a different car, the 2001 Hyundai Accent and 2000 Hyundai Accent. However, it is still accessible from the selected car via links, so may be relevant.
Disconnect Black vacuum supply hose to fresh/recirculated air selector and plug port at selector. Connect vacuum gauge to Black vacuum hose. Start engine. Vacuum should exist at Black hose in all mode positions. In panel position, vacuum should exist at Black and Yellow hoses.
In panel/floor position, vacuum should exist at Black, Blue and Yellow hoses. In floor position, vacuum should exist at Black, Blue, and Red hoses. In floor/defrost position, vacuum should exist at Black and Blue hoses. In defrost position, vacuum should exist only at Black hose. Replace airflow selector if it does not test as specified.