The defroster is a specialized mode of the HVAC system that directs treated air to the interior of the windshield and in many cases to the side windows.
The defroster is usually used to heat and dry the interior surface of the windshield. This removes moisture from the inside to eliminate fogging and also warms the windshield to prevent water from freezing on the outside.
An improperly operating defroster can impair your vision and your safety. Common defroster problems may include little or no airflow to the windshield, inability to change air temperature, and poor defogging. Many import cars have an outside air/recirculation air control lever. The defroster cannot properly remove moisture from the interior of the car unless the lever is set to the outside air mode. If basic checks do not reveal the cause of your car's defroster problem, have it looked at by a professional service technician.