Got A Bad Smelling Air Conditioning System? Here's How You Fix It

Does your car smell like a dirty old sock when you turn on the air conditioner? Or maybe a musty, moldy old attic? If so, you've probably got some mold growing in your vehicle's air conditioning system.

Here's how you fix the smell, and how you can keep it from coming back.

First, Where Does This Smell Come From?

When your air conditioner is used, condensation can accumulate inside. If the system is shut off, whatever condensation inside the system can collect into a small puddle of water (or more than one small puddle) inside the nooks and crannies of your air system. Given enough time, mold will grow in any moist, enclosed space.

How You Can Fix The Moldy, Musty Smell

About 90% of the time, the fix for your moldy or musty smell is super simple.

1. While your vehicle is parked, start your engine and turn your internal air up to the highest setting, and make sure the A/C is on*.
2. Step outside your car, and locate the air vents that your vehicle uses to 'pull' in outside air for the A/C system. Usually, they're right at the base of the windshield.
3. Spray deodorizing spray (Lysol, Febreeze, etc.) liberally into these vents.
4. Check inside your car to make sure you can smell the deodorizing spray coming thru the air vents.
5. Let the vehicle run for 10-15 minutes, periodically spraying more deodorizing spray onto the vents.

*NOTE: Do not use the 'max A/C' setting, as this forces air to recirculate rather than pulling air from outside the car. You need air pulled in from the external vent for this trick to work.

After 15 minutes, you should only smell the deodorizing spray. You can then turn the car off. Usually, one session is enough to eliminate this smell.

What If This Trick Doesn't Work?

If the deodorizing trick doesn't work at all - if your A/C system isn't smelling even a little bit better - something isn't right. This trick always helps, even if it doesn't cure the problem. Be sure to check if your car's A/C system was set to recirculate or not. If it was, the car wasn't pulling air in from the external vents.

But if you're not happy with the result after a couple of tries, take your vehicle to your local repair shop and ask for an A/C system cleaner and service. They can use some more aggressive chemical cleaner and deodorizer specifically designed for vehicles (BG Frigi-Fresh is one example, but there are others).

And, if that doesn't work, you can start replacing parts of the A/C system to eliminate the mold. However, it usually doesn't come to this.

How To Prevent The Moldy, Musty A/C Smell From Coming Back

Mold can only grow if your system has water in it. You can prevent water from collecting in your system by drying it out each time you park your car. Fortunately, this is easy:

1. Before you turn off your car, turn off your air conditioner.
2. Do not turn off the airflow, however, you want to let the interior fan continue to blow air out of the system for 1-2 minutes.
3. Once the air coming out of the dash has warmed up to the same temperature as the outdoors (or close to that temperature), the A/C system is mostly dried out. You can now turn off the air system and turn off your car.

If you don't want to sit in your car for 1-2 minutes waiting for the air, you can just remember to turn off your air conditioner a couple of minutes away from your destination. By the time you park your car, the air coming out of the dash will probably be warm and the system will be dry.

A/C mold and musty smells are a common problem. While automakers like Toyota have been treating A/C system parts with anti-fungus coatings for years - and designing them to drain any remaining water out of the system - car owners have to do their part too. If you take precautions, moldy smells should go away permanently.

Of course, there are other reasons your car might be smelly. Check out this article on how to eliminate other odors.