Today's class: ridding your car's air-conditioning ducts of dubious odors.

Dear Car Talk

Dear Car Talk | Sep 01, 2007

Dear Tom and Ray:

How do you clean the air-conditioning ducts in your car? Thank you. -- Deanne

TOM: The best way to do it is with a spray product, Deanne. The ducts are a nightmare to take apart, so you want to avoid that if at all possible.

RAY: I'm assuming you have a smell coming from the ducts. Otherwise, why would anybody ever think of cleaning their air-conditioning ducts? In any case, there are a number of products available at any auto-parts store that are designed to do just that.

TOM: You turn the key to the "run" position, crank up the fan full blast, and then you spray the stuff into the fresh-air intake, which is near the cowl -- where the hood meets the windshield. If you're not sure where the cowl is, it's where all those leaves and twigs collect.

RAY: So you spray the stuff at the air intake, it gets sucked in, travels through the ducts, where it kills mold and mildew, and ends up in your passenger compartment, where it gives you brain lesions.

TOM: Actually, we have no idea what's in the stuff, but I'm sure the instructions tell you to open the windows and let the car air out before closing it back up and driving in it.

RAY: But the fact that the stuff does end up in your passenger compartment is a good reason not to experiment with household cleaners, like bleach. Because anything that goes into those ducts will end up in your lungs -- even if it is in small quantities.

TOM: If that doesn't work, Deanne, the smell might be coming from the AC evaporator, where water can collect if the drain is clogged. In that case, your mechanic can unclog the drain and then use a product that gets injected directly into the evaporator case.

RAY: If neither of those approaches kills the smell, it could be coming from a mouse or other small varmint that, unfortunately, happened to meet its maker in your AC vents. In which case, we suggest nose plugs for the next eight weeks, or a fire.

TOM: And by the way, Deanne, if your car has a cabin air filter, this would be a good time to change that, too. Good luck.

Get the Car Talk Newsletter