Fog on the inside of the Windscreen

How to Defog the Windscreen –

  • Do not drive distracted, constantly fiddling with knobs on the dashboard.
  • Avoid wiping the window with hands unless it’s an emergency – it will leave unnecessary marks all over the windscreen.
  • Rubbing the windscreen with your sleeve to remove some of the condensed water vapour will not do much – more vapour will condense from your next breath and fog it right up again.
  • Does not drive with the fan set at “recirculate”? This is simply re-using air inside the car – the relative humidity of the air in the car will keep rising.

What to Do – Your air condition in your vehicle must work.

Defogging the windscreen is all about regulating the temperature and humidity inside the vehicle correctly. The bigger the difference between the air and window temperatures, the lower the relative humidity that will still fog the windows up.

Vehicle owners are familiar with cleaning the outside of the windscreen, yet mostly neglect the inside. To fight against continual fog and condensation it is important to clean the inside of the windscreen as well.

  • Blasting the heat

Your windscreen will be much colder than the air inside the vehicle, especially with cold rain or snow hitting it while driving. You need to direct the warm air from the vents against the windows to compensate for this.

This will raise the temperature of the windscreen –but will only work if the vehicle is sufficiently warmed up. Use the defrost/defog vent and crank it to high. Heating the air will dry the windscreen a little through evaporation, but may also add more moisture in the air.

  • Using the Air-conditioning

Most drivers are aware of the benefits of air-conditioning as a way to cool things down, but do not know that their air-conditioning is also capable of producing hot, dry air. Air-conditioners cool your car on a hot day by removing water vapour from the air inside the car, which reduces the temperature of the air. Operating your air-conditioner will immediately start removing water vapour from your car on a cold morning too. The warm, moist breath will disperse into the air inside the car rather than condensing on the windscreen.
Your air-conditioning is also a dehumidifier. So even while using warm air to defrost the windscreen, make sure the air-conditioning is turned on so your car will dehumidify the air before it warms it. Cool air from the air conditioner will dry the air, removing the moisture. The cool dry air will flow over the windscreen sucking further moisture off the windscreen.

“The best way to operate the air conditioner is to start it on cold and then as the air in the car dries out, you can slowly increase the temperature.

Drive Alive – Defogging/Demisting.

  • Leave the air conditioning on until the moisture evaporates from the car. Condensation may form on the outside of the vehicle, because now the glass is colder than the air outside. Turn on the windscreen wipers if this occurs.
  • Adjust the air conditioner dial to a lower setting as soon as the moisture clears from the glass.