Why does AC and heater blow air through defrost vents and will not blow air into cabin vents on 2002 Oldsmobile bravada?

If the AC and heater in a 2002 Oldsmobile Bravada are only blowing air through the defrost vents and not into the cabin vents, it could be due to a malfunctioning mode door actuator. This actuator controls the airflow direction and may be stuck or broken, preventing proper airflow to the cabin. Additionally, a vacuum leak in the HVAC system can also affect the distribution of air. It's advisable to have the HVAC system inspected to determine the exact cause and resolve the issue.