Why Does My Car Smell Bad?

ac smells bad
Laughing at bad smells coming from the air conditioning?. Getty

A bad smell coming from air conditioning vents has become an increasingly common complaint. It seems that this type of complaint is coming from owners of late model cars and almost always cars with R-134 systems.

This is not a new problem; it's been around ever since there have been air conditioners in cars. But if this is an age-old problem, why is it becoming more common? Before we can figure out how to get rid of that smell, 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, the 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.

How Manufacturers Are Addressing the Problem

Are the automakers aware of this problem and are they doing anything to address it? The answer to both questions is yes. They have attacked the problem with both mechanical and chemical solutions.

Ford offers a Purge Module for many of their cars to attack the problem. What it does is to 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 air conditioning in the particular car. The part number for the module is F8ZX-19980-AA and you can inquire about it at your local Ford dealer.

General Motors has a similar system called Electronic Evaporator Dryer (EED).

The EED turns the blower motor on and off in 10-second bursts where 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.

If you don't want to go through the expense of having a special system installed to combat the odor problem, there are several chemical solutions. Some of the chemicals are good for short or long-term use. Lysol is the most common product that is used. The drawback is that that it does wash off and has to be reapplied every few days.

Useful Products

There are other products that will prevent the problem over the long term. They do take special techniques to apply and are generally available only to service professionals.

One such product is called Clean 'N Coat. It is a two-part chemical 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.

There are now about 11 automakers that are now using the evaporator coating method so there must be something to it and hopefully, the problem will diminish as the technology becomes improved and more widely used.

Another product is called Cooling Coil Coating. It is very similar to Clean 'N Coat but requires more specialized equipment to apply.

One other product I'd like to mention is called "Frigi-Fresh" made by BG and is available at most new car dealership parts department. This does work pretty well and doesn't need any special methods to apply it. However, it is not a long-term solution although it will last longer than Lysol.​

Edited by Matthew Wright