Incorrect Temperature Output
WARNING: This page is about a different car, the 1997 Suzuki Esteem. However, it is still accessible from the selected car via links, so may be relevant.
Control cable is broken or binding. Check cables, and adjust them as necessary. Air damper is broken. Repair air damper. Air ducts are restricted. Repair ducts as necessary. Heater core is leaking or clogged. Replace or flush heater core. Heater hoses are leaking or clogged. Replace heater hoses.