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19th Annual Technical Forum: Filters

By Larry Carley

Where is the cabin air filter located?

A. It depends on the vehicle. The majority of late model cars, light trucks and SUVs come factory equipped with a cabin air filter (or, in the case of some Ford vehicles, a slot where a filter can be installed). But there are still many vehicles that do not have a cabin air filter.

Cabin air filters were introduced back in the mid-1980s in Audis and other European luxury vehicles. The first domestic applications date back to 1994 (Ford Contour and Mercury Mystique). By 2005, cabin air filters were installed in nearly 80 percent of all new vehicles. But in some cases, such as 2003 and later GMC fullsize SUVs, the cabin air filter was discontinued when GM redesigned the HVAC (heat, ventilation & air conditioning) system (why, we don’t know).

On vehicles that do have cabin air filters, it is usually located somewhere behind the glovebox in the plastic HVAC housing, or in the cowl area at the base of the windshield where the outside air inlet for the HVAC system is located. Accessing the filter may require removing the glovebox, or a plastic cover in the cowl area.

Refer to the vehicle owner’s manual for the location of the cabin air filter (if the vehicle is so equipped).
Because of its hidden location, many motorists are totally unaware their vehicle even has such a filter, let alone how often it should be replaced.

Cabin air filters trap pollen, dust, smoke and other pollutants that would otherwise enter the vehicle and possibly irritate the nose and lungs of the driver and passengers. The filter also helps keep the A/C evaporator clean so dirt and mold don’t build up on its surface and reduce cooling.

Most of these filters are highly efficient and have electrostatically charged fibers that do an excellent job of trapping even the smallest particles (down to 0.3 microns!). Most cabin air filters will stop 100 percent of all particles that are 3 microns or larger in size, and 95 to 99 percent of particles in the 1 to 3 micron size range. Some cabin air filters also trap odors, and are called “combination” filters. These type of filters have an extra layer of activated carbon that reacts with odors and other airborne pollutants to neutralize them before they become objectionable. The filters can even reduce the levels of carbon monoxide and oxides of nitrogen from the exhaust of other vehicles.

Some cabin air filters are also treated with a chemical biocide or a special surface treatment that destroys bacteria, fungus and mold spores on contact. This is important to prevent the growth of unwanted organisms and odors.



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