Why Does My Car Smell When I Turn On My Air Conditioner?

First, let me reassure you, the smell is not coming from you. Second, if your car sits outside all the time, the odor can be even worse. But don’t worry, we can help!
Air conditioners have a cold component behind your dash area called an evaporator. This is the part that makes your cabin air colder. And just like that icy cold glass of sweet tea on your table, it sweats… a lot. In fact, it sweats so much, there is a specialized drain for the case the evaporator sits in. This thing leaks water all the time because the evaporator sweats; making it a great environment for bacteria and mold to grow. And, again, if your car sits outside where it gets up to 90 and 100+, these things grow and multiply. Pretty soon things start to smell. And to make matters worse, all the organic matter in the air like pollen, leaves, seed pods, insect parts, and dander can find their way into the evaporator case turning it into a warm, moist, dark, microbial kegger for mold and bacteria. There is a filter (sometimes called a pollen or cabin air filter) that keeps a lot of these undesirables out but that can start to smell foul too when it gets filled with this debris.

Helpful tip #1: Replace the pollen filter. This is cheap and easy. Volkswagen recommends doing it every couple of years or 20,000 miles. The new maintenance schedules can stretch out to 60,000 miles, but that is like replacing the A/C filter in your house every three years!

Helpful tip #2: Get the charcoal filter. There are a few types of filters in Volkswagens. Some are plain paper like your house A/C and some are charcoal impregnated. The charcoal helps with odors and is similar in price to the plain paper ones. If someone will not sell you a charcoal activated cabin or pollen filter, go somewhere else.

Helpful tip #3: If you have severe allergies replace the filter every year preferably right after cedar season!

Helpful tip #4: If none of this helps and the microbial kegger has been going on for a while, you will want to treat the interior of your evaporator system with an antimicrobial chemical. Replace your filter at the same time for the best results.

I always tell everyone to fix safety related items before you fix the optional or secondary concerns. With ambient temperatures continuing in the three digits, air conditioners become safety items especially for very young or very old passengers. These tips are meant to be helpful in making owning your Volkswagen something to smile about.

As always, Happy motoring.

Tom Fornshell