Nothing can ruin a drive faster than foul smells blowing from your car’s air vents. If your A/C system is blowing musty, mildew smells, there’s a decent chance there’s bacterial growth inside. And there are other smells too, each with a unique cause.
Read on to discover the most common causes of bad smells from your car air conditioning system – and most importantly, what you can do to get rid of those smells, or at least MINIMIZE the smells.
How Does a Car AC Work?
The air conditioning system for your car is often referred to as the climate control system (CCS). On a modern car, the CCS will run continuously when the engine is running (except for electric cars).
You can think of the CCS as the car’s HVAC system on steroids, where the climate control will automatically keep you at a desired temperature setting.
When the CCS system is working, it normally pulls outside air into the system and either heats that air or cools it, dehumidifies it, and then pumps it into the cabin of the car. Quite the luxury on those bitterly cold winter days or blistering summer heat.
Most cars today have some sort of air filter in this system. This helps to reduce the dust, pollen, and bugs from entering the cabin of the car. The filter element will slowly build up particulates and will need to be regularly cleaned or replaced.
When you utilize the recirculation mode on your CCS, the air you are breathing inside the car is recirculated as the outside air vent is closed. For many modern cars, the recirculation mode will turn off automatically after a short time.
The outside air vent will then open and allow fresh air to flow to maintain an acceptable amount of fresh air circulation as you drive.
Why Does My Car’s AC Smell Bad?
Your car’s air conditioning system, when dirt and bacteria accumulate, can create a damp smell that flows from your car vents.
If the air conditioning has not been used for a while (during winter, for example), mold and bacteria can develop and grow in your air vents, and you get a strong, smelly, foul air when the air conditioning is turned back on months later.
This is the most common reason for this air conditioning smell and usually can be remedied with an anti-bacterial cleaning of your car’s air conditioning filters at regular intervals.
Types of Smells From the Climate Control System
You may smell certain odors in your car, whether your vehicle is new or a few years old (pre-owned).
Note: A new car should have no smells coming from it. If there are, return it to the dealer to take advantage of the warranty.
A mildew, musty, or vinegar (sour) smell. Or a smell resembling a wet dog. The smell resembles that of old socks or a damp t-shirt that has been left unwashed on the basement floor for a week or two.
- A smell of engine antifreeze or oil.
- A smell of engine exhaust and/or rotten eggs.
- A smell of gasoline or diesel fuel.
- A burning smell.
- A cigarette or cigar smoking smell.
Be aware, many of these types of smells may be present inside your car but not in the Climate Control System (CCS). Musty smells and cigarette/cigar smoking smells are the most noteworthy smells that can be classified as follows.
Why Does My Car A/C Smell Bad?
#1. Mildew, Musty, or A Vinegar Smell.
These smells could originate from the cabin air filter, evaporator coil in the climate control system, or possibly, from within the system ducts.
Because the climate control system (CCS) is removing moisture from the air, the moisture in a dark environment can support the growth of mold and mildew. These organic growths can create fungi, bacteria, and other odor-causing chemicals. Generally, as the car ages, the opportunity for an odorous condition increases.
A similar condition can occur on the fabric, carpet, and/or floor mats of the car. Excess moisture in any car can cause any cloth or carpet to harbor bacteria that will release those types of odors, especially in damp winter types of climates
#2. Antifreeze or Oil Smell.
Antifreeze and/or oil can leak from “under the hood”. If these respective leaks happen, the odors may be picked by then picked up by the CCS air inlet located in front of the windshield and delivered to the interior cabin.
Antifreeze can leak from the CCS heater coil and deliver a strong antifreeze odor into the cabin. When the leak is from the heater coil, it may be possible to see antifreeze leaking into the right (or left) front footwell of the car.
#3. Engine Exhaust or a “Rotten Eggs” Smell.
The CCS inlet can deliver the engine exhaust entering the cabin when the car is first started.
When a car exhaust smells more like rotten eggs, or hydrogen sulfide, this can be caused by the exhaust smell, as the engine catalytic converter is not working properly. Like engine exhaust, this rotten egg odor may be found at the CCS inlet.
#4. Gasoline or Diesel Fuel Smell.
The gasoline or diesel odors may also get into the car cabin through fuel leaks from the engine, fuel lines, or the tank, now may have a different effect.
While gas or diesel odors outside of your vehicle can be a serious issue, fuel odors in the cabin should be a concern and addressed right away.
#5. A Burning Smell.
Burning odors can again be drawn into the cabin. Some burning odors may come from the engine area and exit from the CCS inlets at the front of the windshield. Burning odors from the wheel area (ie, brakes) can also get into the cabin.
#6. Cigarettes – Cigar’s smoke.
Cigarette/cigar smoke odors can occur and embed into any car and will leave odors that can last (even if only cigarette/cigar “smoke” is used occasionally). The airborne chemicals used in the smoking will stay and create a biological layer of residue on non-wood interior components.
When the CCS is set to recirculate, the odor layers will episode into all the surfaces of a car’s air handler system, including various potential duct areas or coils.
7 Ways to Prevent Bad Smells in Your Car
Now that we’ve covered how to eliminate bad smells, are there ways to reduce the chances of bad smells developing in the first place? Yes, for the most part. If your car smells clean today, your actions can make it smell cleaner for several years from now.
#1. Always Use the CCS.
Always use the climate control system when you drive your vehicle. Many owners turn the system off, thinking they will save some fuel.
Sure, you may save a couple of bucks a year, but fresh air moving through your car when you are driving keeps the cabin aired out and dry. This helps reduce mold and mildew from occurring in the CCS.
#2. Park in the Sun.
If you park outdoors, choose areas in the sun, not the shade. Mold and mildew will not do well in a UV environment. If a shady space is available, you just may leave the mold and mildew growth areas behind.
#3. Limit the Use of the Recirculation Feature.
This is a neat feature when driving out in the countryside, especially when approaching someone’s dairy farm, or if you need to cool or warm the interior temperature fast!
But the drawback is that it inhibits fresh outside air from moving through your car, which can promote mold and mildew growth.
#4. If You Smoke, Open the Windows.
If you smoke, smoke in the open, and with the windows cracked open to allow the smoke you breathe (and eat in many cases) to vent into the whole great outdoors.
Some of that smoke will be absorbed by your car’s interior surfaces, but it can only get worse if the smoke has no way to escape!
#5. Dry Out Floor Mats.
In wet or snowy weather, when water or snow has soaked the floor mats. Remove the mats and leave them outside to dry overnight.
Wet mats that sit in the cabin’s footwells are an excellent breeding ground for smelly mold and mildew. Dry mats will have much less inclination to do this.
#6. Get any Fluid Leaks Fixed ASAP.
If you have leaking antifreeze, oil, or fuel (gas or diesel), you will know it when you drive a car back into the garage to park overnight, since you will immediately smell it when you start your car in the morning.
Once you smell anything all the time, you should have a qualified technician diagnose and fix it as soon as possible, right after you smell it!
Keep in mind that leaking fuel will present a significant fire hazard as fuel-soaked vehicles can soak and burn to the ground. Constant exhaust odors only indicate that a health hazard exists inside your car, and therefore, must be quantified to get it corrected.
#7. Change Your Cabin Air Filter.
Use the manufacturer’s recommendations and change your cabin air filter periodically. This should usually be completed on an annual basis. Changing out an old filter may rid you of some invisible but smelly mold or mildew source.
You can normally get new elements from your dealer or at most auto parts stores. Since we are discussing your owner’s manual, check it out for further details regarding this filter and the owner’s recommended frequency of changing.
How to Remove Smells from Your Car A/C
To eliminate bad odors from your vehicle’s Climate Control System (CCS), your cabin air filter needs to be changed out, following which, it will need to be disinfected and cleaned. Here are two methods for cleaning out your CCS.
#1. Using an Air Conditioner Cleaning Product.
First, use any of the many automobile air conditioning cleaning spray products available online or at your local auto parts store. German-made Nextzett Klima Cleaner Pro is said to be one of the best, while Armor All Freshfx is a decent, cheaper alternative.
You can apply such specialty sprays through the intake and/or in the ducts as well, and then operate the system and let your vehicle’s A/C system work it through the ducts and coils. Follow the manufacturer’s directions at all times.
#2. Clean the Evaporator Coil.
Second, perform partial disassembly of your auto Climate Control or HVAC System to expose the evaporator coil. Usually, this means you will have to take out the fan housing and fan assembly.
This process could become complicated and is probably beyond the average DIYer. But if you do got down that road, you can use one of the many mold/mildew removing sprays available.
The process will require applying the cleaning product directly to the exposed evaporator coil. Follow the manufacturer’s directions.
Depending on the original malodor issue, you may need to use one of these treatments multiple times over the period to completely remediate the odor.
How to Remove Smells From Car Interiors
In this situation, it’s best to use an aerosol deodorizing product designed for automobiles. Meguiar’s Air Re-Fresher is a great choice. Almost all aerosol deodorizing products are used this way:
- Choose a warm, dry day. Park the car outside, keep the windows closed, and run the engine on the AC setting, aiming at Recirculate mode.
- Place the deodorizing canister inside the car, with the aerosol nozzle locked open so it dispenses the chemical everywhere. You need to make sure all the windows are closed, the doors are closed, and leave the car once the product is dispensing.
- Once that’s done, ventilate the car with the windows down and running the CCS. This process will probably need a wiping down and cleaning the windows inside the car also. Follow all the manufacturer’s instructions and warnings on the product.
If the smells are really severe, you may need to perform the above process several times before you eliminate the odors. Also, you want to try other techniques to solve your smell problems.
The Final Word on Smelling Car AC
Don’t flush the AC case with any caustic drain cleaners. You could ruin expensive-to-replace AC parts. Also, don’t always run the AC in only ‘Recirculate’ mode because then you are preventing fresh outside air from coming in through the AC ducts.
Introducing fresh air into this area can help dry out any excess moisture.
As part of your regular maintenance plan, the make of the car and the vehicle itself doesn’t matter, it’s be informative to turn the AC fan only on for a minute or two, with the engine off and key “on,” to try and run the last bit of water out of the AC case.
In addition, you may want to check with your dealer service department, as many companies have after-run kits that run the AC blower motor for a couple of minutes after the car is turned off.