Cabin filters have
been used on some on Audis and other European makes since the
mid-1980s, and on a growing list of domestic makes since the mid-1990s.
Today, close to 80 percent of all new vehicles have one of these
filters or a place where one can be installed. But it’s often called
the “hidden filter” because many motorists don’t realize their vehicle
has a separate air filter for the passenger compartment. Cabin air
filters are put there for the health of the vehicle’s occupants.
best way to tell if a vehicle has a cabin air filter, or factory
provisions for installing a cabin air filter, is to check the vehicle
owner’s manual. Also check the catalog listings for cabin air filters
by year, make and model.
If a vehicle has a cabin air filter, it
will usually be located at the base of the windshield (open the hood
and look in the cowl area for a small access door), or somewhere behind
the glove box in the HVAC assembly (look under the dash for an access
door). On some vehicles, the glove box has to be removed to access and
replace the filter.
Most cabin air filters are flat panel filters,
but some have unusual shapes so they will fit the HVAC inlet duct. Some
may also be in two sections to make replacement easier. These filters
can 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.
Many motorists are not aware their vehicles
have these filters. So ask your customers if they have checked their
cabin air filters lately. It may stimulate some conversation as well as
The service life of a cabin air filter depends on two
things: the type of filter (dust or combination dust/odor) and
operating conditions. A filter on a vehicle that is driven frequently
on gravel roads will not have the life of a filter in a vehicle that is
driven in a cleaner environment. Exposure to heavy traffic (especially
diesel fumes) and urban pollution can also shorten the life of a
combination dust/odor filter.
As a general rule, most cabin air
filters should be changed every 20,000 to 30,000 miles or more often
depending on the size and capacity of the filter. Many vehicle
manufacturers recommend replacing the filters every 12,000 to 15,000
miles or once a year. Refer to the vehicle owner’s manual for specific
service interval recommendations.
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 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.
levels of these pollutants can be quite high in heavy stop-and-go
traffic, and it’s not unusual for the concentration of these pollutants
to be several times higher inside a vehicle than outside. Studies have
shown that driver reaction times are slower when the driver is being
affected by poor air quality.