A musty or moldy smell from the discharge vents is a common problem on vehicles with air conditioning. More than unpleasant and annoying, it can also trigger allergic reactions. This problem occurs when condensation (water) from the evaporator collects on the evaporator fins and also when the water settles in the bottom of the evaporator housing. The water attracts dirt from the air, and together, along with the dark location, they serve as the perfect breeding ground for mold. Although the water should drain from the evaporator housing through a drain tube that passes through the floorboard and outside the car, this drain tube can plug with debris and cause a backup of water into the evaporator housing. Sometimes the water spills over into the vehicle's interior. It all depends on the severity of the blockage. Even with proper drainage, there is still enough condensation present on the evaporator fins and within the evaporator case to enable mold growth.
You can combat mold (and odor) by attacking the problem at its source. First, make sure the evaporator drain tube flows properly. With the A/C system operating, you should see a discharge of water from the tube below your car. However, even if there is drainage, it may not be sufficient as the tube could be partially restricted, causing a back-up into the evaporator case. You will find the tube located directly below the heating/air conditioning case, where it passes through the floorboard to the outside. The tube is made out of a flexible rubber material. Inspect the tube closely from underneath and look and feel for debris in the end. Sometimes, mud and other road debris may collect on the end of the tube and impair proper flow. Clean the tube as needed to restore proper flow.
The next step is to treat the mold itself (the heart of the problem). To do this, you treat the evaporator core with an anti-microbial chemical that attacks and kills the mold. You can do this with some products by spraying them into the A/C vents and air intake. Others require that you apply them directly to the evaporator core itself with a special applicator wand or nozzle. In extreme cases, the evaporator may need to be removed for cleaning, but this is rare and best left for professional service technicians.
The most important thing is to make sure you use a chemical that actually kills the mold and follow the directions exactly for that product. Simply treating the problem with a deodorizer will only mask the odor for the short term. For best results, the evaporator should be treated annually.
Here are a few other tips that may help the mold problem from reoccurring. First, turn off the A/C, then switch the blower to the high setting, and move the air control (if applicable; often used on Japanese imports) to the fresh (outside) air mode. Doing this for about the last 10 minutes of operation can help dry the evaporator and case, helping to curb the breeding ground for mold. Running the system normally in the fresh air mode, rather than the recirculation mode, may also help to reduce the chances of mold formation. Finally, if your car has a cabin filter, make sure it's changed on a regular basis (usually every 15,000 miles). Excessive dirt entering the evaporator case gives mold extra "food."
A diagnosis by Kirtec Auto Services can pinpoint your specific problem for which we can then perform the correct remedy.