Heater Unit
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.
Heater unit houses heater core, vent/defrost mode door, temperature blend mode door, and fresh/recirculated air mode door. Coolant flows continually through heater core. The amount of heat is controlled by blending air across heater core with fresh/recirculated air being vented to selected outlets. See Fig 1.