How often should you replace your cabin air filter?

A clogged cabin filter weakens A/C, heating, and demisting.

A blocked cabin filter chokes airflow from the vents, which cripples demisting exactly when you need it in cold wet weather. Damp organic debris trapped in the media also grows mould, which is the usual source of a musty smell when the fan starts.

1. Locate the housing. Most commonly behind the glovebox, sometimes under the bonnet at the base of the windscreen, occasionally under the dashboard.
2. Release the glovebox. Usually a damper arm and side stops, so it drops further than normal. No tools needed on most cars.
3. Note the airflow arrow. Same principle as any filter. It usually points downward. Photograph it before removal if unsure.
4. Withdraw the old filter carefully. It will be holding leaves, grit and insects. Have a bag ready and keep it level.
5. Vacuum the housing. Debris collects in the bottom of the box, and leaving it undoes the new filter immediately.
6. Fit the new one and reassemble. Arrow the same way as the old one. Refit the glovebox stops.

• Weak airflow from vents even with the fan on maximum
• A musty or damp smell when the ventilation starts
• Windows demisting much more slowly than they used to
• Increased dust or pollen inside the car
• Fan noise higher than usual for the airflow you get

• Not knowing the car has one at all, and running the original filter for a decade
• Fitting it upside down, which some housings will physically allow
• Skipping the housing vacuum, so the new filter sits on a bed of old leaves
• Paying a dealer a large labour charge for a fifteen minute job

• Dusty roads, gravel driveways and pollen season all shorten it substantially
• Heavy urban traffic loads the filter with soot
• Activated carbon filters cost more and help with odours and exhaust fumes

Only if the housing is under the dashboard and awkward to reach, which is true on a minority of models. On most cars this is a fifteen minute job with no tools.