Symptoms
- Musty or moldy smell when AC or heat first turns on
- Reduced airflow from vents
- Allergy-like symptoms while driving
- No cabin filter change in over a year
Likely causes
- CommonCabin air filter clogged with debris and moistureLeaves, pollen, and dust build up and hold moisture, creating a breeding ground for mildew smell.
- PossibleMold or mildew growing in the evaporator core (AC system)If changing the filter doesn't fix the smell, moisture may be growing further inside the AC housing.
- Less commonFilter never installed on a used carSome used cars are missing a cabin filter entirely if a previous owner removed it and didn't replace it.
What to do
- Find your cabin air filter location, commonly behind the glovebox or under the dashboard (check your manual).
- Remove the access panel or glovebox as needed and slide out the old filter, noting its orientation.
- Inspect it for dirt, debris, or visible mold, which confirms it's the likely smell source.
- Install a new filter in the same orientation as the old one, following the airflow direction arrow if present.
- Run the AC on high with the recirculate button off for a few minutes to help air out any residual odor.
- If the smell persists after a new filter, consider an AC evaporator cleaner treatment or have a shop check the evaporator core.
Tools and parts
Cabin air filter for your vehicleSearch: “cabin air filter for [your car year make model]”
When to call a pro
If the musty smell continues after a new filter, or you suspect mold in the AC system, have a shop inspect and treat the evaporator core.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.