Your Vehicle's Cabin Air Filter

Team BlueStar Inspections
Many vehicle manufacturers suggest your vehicle's cabin air filter be replaced every 12,000 to 15,000 miles, or annually. What is a cabin air filter, you ask? That is a good question considering many motorists don't even know their vehicle has a cabin air filter. It's out of sight and out of mind, but that's not where it should stay. Most vehicles today come factory equipped with a cabin air filter. The cabin air filter is designed to do three things:
  1. Improve the quality of the air entering the passenger compartment through the heating, ventilation, and air-conditioning (HVAC) system.
  2. Catch dirt, dust, pollen, mold spores, smog, and other airborne material that can make riding in a vehicle unpleasant and unhealthy, particularly if you or your passengers have allergies or other respiratory issues.
  3. Keep debris out of the HVAC system evaporator and heater core, thereby preventing them from clogging and becoming ineffective.
Cabin air filter replacement guidelines vary by manufacturer. Check the maintenance schedule in your owner's manual to be sure your cabin air filter is being maintained properly. Manufacturer recommendations are useful guidelines, but remember that the need for replacement will be influenced by how much you drive and the conditions you drive in. For example, if you regularly drive in heavy traffic in urban areas that have poor air quality and pollution, you may need to replace your cabin air filter more often. This may also be true for vehicles used in remote areas or desert climates where large quantities of dust need to be filtered out. Three signs indicating you may need to replace your cabin air filter include:
  1. Reduced air flow through your air ducts, such as when you crank up the blower fan to the highest position and get more noise than results.
  2. There is increased noise in the blower fan when you increase the fan speed. This is due to the fan working harder to bring in fresh and filtered air through the dirty filter.
  3. Persistent foul odors or musty smells in the cabin of your vehicle.
Even if these warning signs are not present, have your vehicle's cabin air filter inspected and replaced at least annually; You may even be able to do this task yourself. Cabin air filters are commonly located behind the glove box and can be accessed by freeing the glove box from its fasteners and following the instructions in your vehicle's owner's manual to gain access to the cabin air filter. Some cabin air filters are located under the dashboard, or under the hood where fresh air enters the HVAC system, and may be difficult to access. If this is the case, have an ASE certified technician inspect the filter the next time you have your vehicle serviced. If a technician recommends you replace your cabin air filter based on mileage or time, ask to see the current filter. Depending on how long the cabin air filter has been in service, you may be shocked at what you see: a filter clogged and covered with twigs, insects, pollen, leaves, soot, and grime. You will be amazed that any outside air was even able to get into the cabin of the vehicle. If you value the air you breathe, the sight of the filter will serve as a visual reminder of the importance of maintaining your cabin air filter. A pre-purchase or used vehicle inspection does not always include the physical inspection of the cabin air filter due to the varying degree of difficulty to remove, but it should assess the air flow and volume from the ducts on all fan speeds, listen to the noise the blower fan makes on all speeds, and detect any foul smells coming from the HVAC system which would indicate cabin air filter issues. Have the cabin air filter inspected before buying a used vehicle, and maintain the filter as recommended by the vehicle manufacturer so you and your passengers can breathe a little easier.