Q: Can you please tell me what the deal is with “cabin air filters”? I normally take care of all the maintenance on our cars but while away at college our daughter took her car in for an oil change and they tried to sell her a cabin filter. Which cars have these? How do they work? How often should they be replaced? Can I do it myself?

A: These filters have been around for a couple of decades in European vehicles and during the past 10-15 years have also been widely adopted in domestic and Asian vehicles. Cabin air filters go by a variety of names and resemble a miniature version of a home furnace filter. The filter is designed to trap pollen and dust passing through the vehicle’s ventilation system, with some additionally claiming to filter allergens, odors, pollutants, soot, carbon monoxide, etc.

A cabin air filter typically lives in a slide-out tray within the HVAC (heating, ventilation, air conditioning) housing behind the instrument panel. Many are easily accessed after uncoupling the glove box and tilting it down/out of the way. Others are accessed from under the hood, or above and to the right of the accelerator pedal. To find yours, consult your owner’s manual or an online auto repair service at a public library, or simply look for the tray.

In most cases, once you determine the location, it’s a simple do-it-yourself job. Replacement filters cost between $10-$30, from basic pleated paper to fancier multi-stage, and are intended to be replaced every 12,000 to 15,000 miles. Higher-end, multi-stage replacement filters containing activated charcoal help reduce odors and toxic gases. They also generally fit better, preventing unfiltered air from sneaking around the filter.

What happens if you don’t regularly renew your filter? You’ll likely notice an odor, then gradually reduced ventilation airflow. If severely restricted, there’s a long-shot chance of damage to the air conditioning compressor because of decreased evaporator function and the return of liquid refrigerant.

Once you see how yucky a cabin filter can become in a year’s time, you’ll want it out of the car for sure. An amazing quantity of sludgy, stinky stuff passes through the ventilation system, largely due to leaf and debris buildup at the air inlet near the windshield/hood intersection. Diligent cleaning of this area as well as under the rear edge of the hood can make a big difference in ventilation air quality, with or without a cabin filter.

Cabin air filters are the best thing to ever happen to the quick-lube industry. With other vehicle maintenance needs becoming fewer, this super-profitable and easy-to-perform service couldn’t have come at a better time. Adding to this, a large percentage of vehicle owners aren’t aware they have a cabin filter, or how simple a DIY job many can be.

How about you pay to have this done once, but insist on being shown where the filter is located? Then you can decide if you’d like to handle it in the future.