Mist on your car windows occurs when the temperature of the glass is cooler than the air inside (or outside) the car. Moisture gathers on the glass as the water in the air condenses on it. Demisting the exterior of the car is as easy as turning on the windshield wipers. However, demisting the interior car windows is a little more complicated. It requires a lowering of the car's internal temperature.
Turn on the air conditioner in the vehicle and set the air flow control (the control on the dash that controls which vents the air comes from) to point toward the windshield. This is also the control to defrost the windshield using the heat. Remember that the heat and air conditioning comes through the same vents.
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 windshield wipers if this occurs. If you are travelling at a high speed, little moisture will accumulate, so this will not be necessary.
Adjust the air conditioner dial to a lower setting as soon as the moisture clears from the glass. If moisture begins to accumulate inside the glass, turn the air conditioner back up to remove it. The point is to find a temperature and humidity level inside the car that prevents moisture condensation.
Turn on the heater at a low setting if turning the air conditioner up does not solve the misting problem in your car. This will raise the temperature of the air inside the car to same level as outside the car, preventing the moisture build up on the glass.
Opening a car window will also help to remove moisture in the air. On humid days, this technique will not be as effective. Use the air conditioning and heat to remove the mist.