Why Does My Car Smell Bad?

Regardless of the cause, here's what you can do about it.

Car ventilation system
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A bad smell coming from air conditioning vents has long been a common complaint with car owners. Some vehicles in particular seem to have been more problematic over the years—like the 2009 Ford Focus. Furthermore, it seems that this type of complaint comes primarily from owners of late model cars and almost always cars with R-134 systems. Since there is still a vigorous trade in the used car market, it helps to know why your car might be doing this.

Bad Air

This is not a new problem; it's been around ever since cars have had air conditioners. Before we can figure out how to get rid of that smell, though, we have to understand what's causing it. The origin of the smell is caused by fungus, bacteria, and other microbes growing inside the evaporator core. The moisture-laden environment is very conducive to the growth of these organisms.

As automakers downsize components to save space and weight, this problem has been increased. Because the automakers made the evaporator smaller, they added more fins and packed them closer together to increase the efficiency of the evaporator. While this has made the evaporator more efficient, it has also made it more prone to trap moisture that contributes to the growth of these organisms.

Purging the Smell

Automakers have long been aware of this problem and have attacked it with both mechanical and chemical solutions.

Ford came up with a Moisture Purge Module that attaches to the A/C unit to dry out the evaporator core. What it does is cycle the blower motor to dry out the evaporator for a period of time after the engine is shut off. The module will work for most Ford cars, but it requires a special harness depending on the type of electrical system used in the car. The part number for the module is F8ZX-19980-AA. Call your local Ford dealer to see if they have any in stock. Or check eBay or Craigslist. 

General Motors has a similar system called Electronic Evaporator Dryer (EED). The EED turns the blower motor on and off in 10-second bursts (whereas the Ford Purge Module runs it continuously). This will save the battery and GM says it pushes out two to three times more moisture from the evaporator. There is also a temperature sensor that will turn the blower motor off when the ambient temperature is low enough that the possibility of microorganism growth is at it's lowest. The EED is not based on what type of electrical system is used; it can be used on any General Motors product without any modifications.

Spray Solutions

There are a few chemical products out there that will help take care of the problem, too. Clean 'N Coat is a two-part system that embeds an antibacterial in an acrylic coating that sticks to the evaporator. It comes in a spray can that you can spray on the evaporator and offers protection for about three years. Call your local car dealership parts department for more information.

There are also a number of products specially formulated as automotive HVAC duct cleaners. Quest A/C System Cleaner, and 4 Seasons Dura II Flush Solvent are just a couple that are currently available at automotive supply stores. And many car owners swear by a good spraying of Lysol every now and then. It's not a permanent solution, but it is quick, easy, and relatively inexpensive.

Other Smelly Causes

Finally, no matter which make or model you drive, if you park your car outside or in a car port where small animals can reach your duct work, you might also have to battle dead animal smell at some point. In this instance, any of the short-term solutions mentioned above should work to help combat the stink.