Cars are built to have a constant flow of fresh air moving through the interior, which helps to maintain a comfortable atmosphere in the car, without needing to open the windows. The air entering the car can be heated by the engine to ensure the windows and windscreen are kept clear and mist free and that the interior of the car is kept at the desired temperature. This is where the air vents come into play.
Air enters the car through the air intake system, situated at the front of the vehicle, and also through the grilles on the bonnet. Air enters the car interior through the front foot-wells and through interior air vents. Interior air vents can be found in the panel at the foot of the front windscreen, which allows warm air to be blown on to the glass which stops the screen from misting up, and there are also interior air vents in the dashboard. At the back of the car there are exit vents allowing air to leave the car.
The interior air vents in the dashboard can be adjusted to direct the flow of air, for example, at the faces of the front passenger and driver. The air flowing through the vents can be cooling, in summer months but can be heated, by the engine, when required, so that the air vents blow out a channel of warm air.
A sign that you need to replace the interior air vents in your vehicle is a nasty odour inside the car. Air vents are a breeding ground for mould and bacteria and can get dirty and clogged up if not cleaned regularly which will cause this part to deteriorate. It's important to make sure you fit a new interior air vent that's compatible with your car so that it will work competently.