Why does the heater work but the defroster won't work on as 1995 Buick Skylark?

If the heater works but the defroster doesn't on a 1995 Buick Skylark, it could be due to a malfunctioning blend door actuator, which controls airflow between the heater and defroster vents. Another possibility is a clogged or damaged defroster duct, preventing warm air from reaching the windshield. Additionally, low coolant levels or a faulty thermostat could affect the defroster's performance. Checking these components can help diagnose the issue.