What causes air to come out of your defrost vents when the ac is on in a 1995 gmc vandura?

In a 1995 GMC Vandura, air coming out of the defrost vents when the AC is on is typically due to the vehicle's HVAC system design, which prioritizes defrosting to prevent windshield fogging. When the AC is activated, the system may redirect airflow to the defrost setting to help remove moisture from the air. Additionally, a malfunctioning blend door actuator or vacuum leak in the HVAC system could also cause improper airflow distribution. Regular maintenance can help ensure the system operates correctly.