The Cause of Bad Smells From a Cars AC and How to Fix It

In this article, we’ll cover topics like what causes bad smells from your car’s AC and how to prevent the smell when you turn on the AC. We’ll take a look at how to clean and maintain your car’s air conditioning.

You can keep your car cool and comfortable in hot weather by turning on the AC. Your car’s air conditioning removes heat and draws moisture out of the air inside your car. This is what makes the inside of your car feel cooler.

Possible Causes of Bad Smells From Your Car’s AC

Sometimes your AC may seem to be working properly, but an unpleasant smell is still released by the system. The cause of the smell coming from your car’s AC can be bacteria buildup on the evaporator located behind the dashboard. As part of its normal operation, the AC pulls in outside air, cools it to a certain temperature before releasing it inside, and in the process accumulates dust from that outside air within itself.

Bacteria and viruses that grow in your AC system are structures that can multiply very quickly and can be harmful, posing a serious threat to your health, particularly to your respiratory system.

Your AC dries the air in your car, but that moisture has to go somewhere. Water droplets form on the core of the evaporator behind your dashboard and then drain to the outside through a drain tube.

While the AC is running, condensation forms on both the evaporator and the AC condenser. When we turn off the car, this condensation liquefies and coats the AC components. Most of this water drains out through the drain tube. A significant amount, however, stays inside.

A humid environment is a perfect breeding ground for mold and bacteria. These are also the cause of the bad smell coming from the AC.

If you’re having a mold problem inside your car, on the seats, or on leather trim, also take a look at our article on this:
SEE ALSO: Preventing and Removing Mold Inside a Vehicle

The Cabin (Pollen) Filter Could Be the Cause of the Bad Smell From Your AC

The cabin (pollen) filter is, by design, a filter that traps dust, pollen, and other allergens from the outside air. If you use your AC a lot and haven’t changed the filter in a long time, these filters begin losing their function over time. As a result, bacteria multiply rapidly. This degrades the air quality inside the car and causes a bad smell in the cabin.

If the cause of the bad smell coming from your car’s AC is the cabin filter, all you need is a new cabin filter.

Could Innocent Visitors Be the Cause of the Smell When You Turn On the AC?

One cause of the smell when you turn on the AC can be animals hiding in your car’s engine bay. Small animals can become trapped in the AC condenser in the engine compartment and be unable to get out, and end up dying there. Checking this area before using your car both prevents smells that could develop in your car and can save the animal trapped there.

Once the animal dies, its remains decompose there and produce an odor, which then gets pushed into the car through the AC system. In fact, this decomposition smell tends to be strong enough that it’s quite noticeable.

How to Get Rid of AC Odor

Up to this point, we’ve covered the causes of the bad smell coming from the AC. So how do you get rid of AC odor?

Replacing the Cabin Filter

The first method that comes to mind should be replacing the cabin filter. Best practice is to replace your car’s cabin filter every 30,000 km. On most cars, replacing the filter is easy and won’t cost you much.

You can access the cabin filter compartment from your car’s dashboard. If you think it’s time to replace the cabin filter, check out the video below.

Video: How to Replace the Cabin Filter

A video explaining how to replace a car’s cabin filter. (above) It’s presented for a 2007 model Toyota Corolla Altis. But since the filter is located in roughly the same place on most other cars, we think this video guide will still be useful to you.

I Did This, but the Air Still Smells Bad!

You’ve replaced the cabin filter but the AC still smells bad. You may need your mechanic or a shop to investigate the cause. Have them check the condenser. On most (though not all) front-engine vehicles, the condenser is right next to the radiator. This position means it’s exposed to everything — water, mud, leaves, and so on. Cleaning the condenser and evaporator and replacing the cabin filter should solve the problem.

Cleaning the AC Air Ducts

There are AC sprays that some users recommend for this. They’re also called an AC bomb (foam cleaner). The windows are closed, the AC is turned on, and the recirculation button is pressed. The cabin filter is removed, and the spray is emptied entirely into the AC’s air intake point in the engine bay. The spray’s contents then travel through the heating system and into your car’s interior. With the doors closed and the engine and AC running, the car is left running for 5 minutes with the recirculation button on. Afterward, a new cabin filter is fitted, the doors are opened, and the car is ventilated.

Video About Car AC Cleaning

Some users apply this type of spray through the interior vents instead. However, online we’ve come across comments from people who damaged the car’s electrical components using this method, or who said the spray sticks to the ducts and makes them more prone to further dust buildup. So only try this method if you’re confident about what you’re doing and have done enough research. Of course, the safest option is to have it done by an authorized service center.

Can AC Odor Be Prevented?

Actually, there is a way to largely prevent this from happening in the first place. Turn off the AC about 5 minutes before you turn off the car. Turn off the AC (AC OFF) but leave the fan running. This way, the airflow through the ducts will dry out the condenser and air ducts and prevent the odor. The whole logic is about trying to keep the system and air ducts dry.

Having your AC serviced and cleaned regularly is quite important for your health, your driving comfort, and the lifespan of your AC.

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