Windscreen Demisting (Defrost)

Fog forms when moist cabin air touches cold glass. The air conditioning dries the air, so demisting works best with A/C on, fresh air and the vents directed to the windscreen. Many cars have a dedicated max-defrost button that sets fan speed, temperature and air distribution automatically.

Warm, dry air absorbs moisture from the glass surface and raises its temperature above the dew point.

Dirty glass and a clogged cabin filter make fogging worse. Persistent fogging and damp carpets can point to a water leak, a blocked drain or a leaking heater core.