Hobbies Cars & Motorcycles Does Your Truck's Air Conditioner Stink? Tips to Avoid or Eliminate Smelly A/C Odors Share PINTEREST Email Print David Lees/Getty Images Cars & Motorcycles Trucks Cars Motorcycles Used Cars SUVs ATVs & Off Road Public Transportation By Dale Wickell Dale Wickell is an automotive expert who has worked in the industry for more than four decades. He currently works for LeMay - America's Car Museum. our editorial process Dale Wickell Updated February 23, 2019 Do you notice a strong, mildewy smell when you first turn on your truck's air conditioner? If the answer is yes, you aren't alone. Why Does My Truck's A/C System Stink? One of the A/C system's most important jobs is to remove moisture from the air. The moisture becomes caught in the A/C's evaporator (a unit in the dash that looks like a radiator) and condenses to water on the evaporator's fins. The water runs down to the bottom of the box holding the evaporator before exiting through a drain tube, where it creates that puddle you see under the truck when you park it after using the A/C. The higher the humidity, the more moisture the A/C grabs from the outside air. Unfortunately, some of the moisture sticks around, clinging to the fins when the vehicle is turned off, and making those damp spots a perfect breeding place for mold and mildew as temps in the parked truck rise. Preventing Mold There's no sure way to completely prevent mold and mildew from developing in the evaporator, but it helps to turn the A/C switch to outside air before you turn the truck off. Doing that allows some of the moisture to escape, and keeps the truck's interior a little cooler than it would be if the switch is left in the recirculate position. If the A/C already has an odor, you'll need to clean the evaporator (it's usually best let a dealer or trusted repair shop perform the cleanse). Cleaning the Evaporator An evaporator cleanse is normally a three-step process. A tube is inserted into the evaporator and used to fill the unit with disinfecting foam. Next, the tech shoots a cleanser into the evaporator box to clear out the foam (and the dissolved or loosened mold and mildew). Finally, an air freshener/antibacterial product is inserted to help discourage build-up of new mold and mildew. A cleanse might be necessary every year or two, depending on the truck, the design of the air conditioning system and the way you use the A/C.