If it weren't for the cabin air filter, all of the dirt, pollen and debris in the air around your vehicle could easily find its way inside. However, the filter can only capture so much before it is full and needs to be changed.

If you do not change the air filter regularly, it will become clogged, which can disrupt the functionality of the vehicle's airflow system, including heating and cooling. Since winter is just around the corner, it can be wise to check the air filters to ensure that you will be able to stay warm when the temperatures drop.

A car's inability to bring hot air into the passenger cab can also create other problems in the winter. The defrost setting on the ventilation system will not work, which can make it exceptionally difficult to scrape ice from the windshield in the morning. The defrost also helps bring up the temperature of the glass to be closer to the interior, which helps to prevent the windows from fogging up.

Air filters also provide clean air for passengers, which is especially helpful for people who have allergies, as they trap pollen, dust and other allergy-inducing particles. This way, passengers can enjoy a sneeze-free trip, but if the filter needs to be changed, allergy sufferers may want to pack some tissues for longer road trips.

The rule of thumb for replacing these filters is at least once a year or every 12,000 to 15,000 miles, but this frequency varies depending on the type of area in which you reside. People who drive on dirt roads regularly or live near the beach will likely need to change their filters more often than drivers who spend most of their time on paved roads and more urban areas.

The majority of vehicles made after 2001 will have at least one cabin air filter - luxury cars tend to have two or three. For the most part, filters tend to be located under the hood or in the underside of the dashboard, generally on the passenger's side. If you cannot easily locate the filters, you can consult the owner's manual for direction. When a vehicle uses more than one filter, they may be grouped together in one area - often placed side-by-side or in a row - or they could be in a varied set of locations.

In some vehicles, the filters are easily accessible, but others may require removal of other parts to reach them. Filters located in other places may require additional tools to remove. When you replace a filter, you should also take the opportunity to vacuum the filter chamber to remove any excess debris that could otherwise blow into the cabin.

There are two basic types of filters, and the kind you choose will depend on your environment. Particulate filters are pretty basic - they keep out dust, debris, pollen, bacteria, mold, spores, and other airborne pollutants. Activated charcoal filters, which have been treated with heat and chemicals, do the same thing, but they also keep harmful gases and other smells from getting inside the cabin. They can be especially useful for drivers who spend a lot of time in traffic, live in densely populated areas or frequently drive past landfills and other stinky locations.