Q: How Does the Front Defroster Work in a Car?

Selecting the front defroster mode directs warm air up through the ducts at the base of the windshield in order to clear moisture in warm weather or frost in colder temperatures. In cold weather, the defroster becomes more effective after the engine is warm and able to send warm air onto the inside of the windshield. On many vehicles, by selecting the defrost position on the controls, it will also activate the A/C compressor. Cooling the air with A/C first will remove more moisture from the air so it can do a better job clearing the windows.

If the A/C system is not functioning correctly this ability will be lost. The chilled, less humid air is then warmed and directed towards the windshield and front windows. Selecting “High” on the fan speed will also make the defroster more effective.

Since some climate conditions can cause rapid fogging of the glass, reliable operation of the defroster system is very important for safe vehicle operation. If you run into any issues regarding this system, have a professional mechanic help you diagnose and fix your defroster.