A cabin air filter is a component of the climate control system in your vehicle. The filter prevents dust, pollen, and other debris from entering the passenger compartment through the heating and air conditioning components. This is similar to the way a furnace filter works inside your home. The filter also helps to remove foul odors that might enter the cabin space.
The cabin air filter is typically made of paper or foam suspended in a plastic frame. Some filters contain activated carbon to eliminate fumes. The cabin air filter is inserted into the ductwork inside your vehicle, in the path of the airflow from the vents. That way, whether the air is coming from outside the vehicle or is being recirculated, it passes through the filter.
Your cabin air filter is at work during all seasons and across a wide range of driving conditions. It collects dust, sand, pollen, and other contaminants so that they do not enter the passenger compartment through the vents, and so that you do not have to breathe them. Other debris also tends to collect in the filter.
For instance, if you park under a tree, leaves, seeds, and small twigs can enter the external vents and end up inside the cabin air filter compartment. Odd odors that pass through the filter can become trapped as well, causing it to smell inside your vehicle. If you notice that the airflow from the vents has decreased, or the smell coming from the vents becomes musty, moldy, or otherwise foul, it is probably time to replace your cabin air filter.