8 Causes of Smoke Coming Out of the Car AC Vents!

(Last Updated On: January 12, 2024)

Are you experiencing smoke coming from your car’s AC vents while driving? This can be a dangerous situation, and taking immediate action is essential. Without knowing what the problem is, you should assume something is burning behind the dashboard, which could pose a fire risk. 

This article will discuss the eight potential reasons for smoke coming out of the AC vents and what to do if you encounter this problem. 

8 Reasons Why Smoke Is Coming Out of the Car AC Vents

Please do not assume that the air con is to blame because smoke is coming through the AC vents. Many electronic components sit behind a dashboard, lights, radio, USB ports, etc., that can fail, meaning smoke will come out of the AC vents, as this is the smoke’s only way out. 

Electrical malfunction

Behind the dashboard is a series of wires and connections that carry power to and from all electrical components in the cabin. If the electrical system is overloaded, the system will usually blow a fuse, which disables the component the wires lead to. However, the wiring may heat up, and the plastic connections may melt before the fuse blows. This can result in small amounts of smoke and a burning smell coming through the AC vents. 

It is important to note that this is a serious fire risk; a fire behind the dashboard can spread quickly, just like a house fire.

Clogged cabin filter

The cabin filter filters the air that enters the cabin through the HVAC (heating, ventilation, and air conditioning) system. Over time, this filter can become clogged with dirt, dust, and other debris. When the filter is clogged, it can restrict the airflow through the HVAC system. This, in turn, causes the AC system to work harder than it should to cool the air. As a result, the components of the AC system can become overheated. If this continues for an extended period, they can start to burn. The burning components can produce smoke, which may come out of the dashboard and the AC vents.

If a clogged cabin air filter is determined to cause the smoke, it must be replaced promptly. Replacing a cabin filter is a simple task that most people can carry out at home; the filter can usually be found just below the glove box and removed behind by undoing two screws, sliding out the filter, and replace with a new one. 

Failed blower motor

The blower motor pushes the air into the cabin through the AC vents. The most common reason for blower motor failure is the accumulation of debris in the blower fan system, causing the blades to get stuck and the motor to overheat. When this happens, you may notice the smoke given off by the motor as it burns out coming through the vents. 

One of the other signs of blower motor failure is unusual noises such as grating or screeching when the blowers are on. If you hear these noises, immediately switch off the blowers; this will cool the motor down and stop any potential fire risks. It is also important to not keep the blowers turned off until the blower motor is replaced. 

Burning debris in the ventilation system

Burning debris is the most common reason for smoke coming from the heater vents. The biggest suspect is old car park tickets left on the dashboard. They fall behind the dash and get burned on the heater matrix or electrical components, causing the smoke to come through the dashboard. Providing they don’t cause a fire while burning away, you will rarely experience any other problems after. 

It’s important to remember to remove old parking tickets and anything flammable that can fall behind the dashboard before driving. 

Faulty AC

Behind the dashboard is the AC evaporator, which cools the air blown into the car’s cabin. The evaporator absorbs heat from the warm air blown over it, giving you the cold air blowing through the vents. As the heat is absorbed, the refrigerant inside the evaporator turns into a gas and is then sent to the car’s compressor, which is compressed and turned back into a liquid. If you get a leak on the evaporator or the pipework leading to or from it, the AC refrigerant will spit out the gas coming through the AC vents, looking like smoke. You can tell it’s AC gas by its unusual smell. 

When your car’s AC system leaks, there is usually nothing you can do to prevent the AC gases from coming through the vents. You have to wait it out. However, it is highly recommended not to drive the car until the leak has completely stopped. This is because the AC gases come out at a high velocity.

To prevent the gases from escaping, it is best to use an AC machine to drain the system quickly; however, that’s only possible if your cars are in a garage with an AC regas machine to hand. If you’re driving and notice the leak, it is best to pull over, get out of the car, and let the gases escape, as they are dangerous to breathe. AC gases harm the ozone layer, so you must take precautions to prevent them from escaping into the atmosphere where possible.

ac button

Oil or coolant leak

If oil or coolant leaks from the engine and drips onto a hot component, it can burn and produce smoke. This smoke can enter the cabin through the AC vents, and you may also smell the burning oil or coolant. The radiator, coolant hoses, oil pipes, and oil filter are common places to check for oil or coolant leaks.

Regularly checking your car’s oil and coolant levels is essential to help identify potential issues. Modern vehicles have dashboard indicators for low oil or coolant levels. If one of these lights is on, it could be the reason behind smoke coming through the AC vent.

Mold

Mold growth is a common issue I see regularly, causing problems for car interiors. This can occur due to faulty weather stripping, the spare tire well being full of water, or a fluid spillage in the cabin. Mold spreads quickly and can even reach the behind dashboard. 

Although it may not directly cause smoke to come through the AC vents, it can cause problems like contaminating electrical components, causing them to overheat, or the car cabin filter to clog up, leading to the blower motor overheating and struggling. Both of these, which we’ve earlier highlighted, will cause smoke to come through the vents.

Heater core failure

The heater core is a small radiator behind the dashboard responsible for heating the air in the cabin. It works by heating the air passing through its core, which has hot engine coolant passing through it. 

When the heater core fails, it can leak coolant into the cabin or onto the electrical components behind the dashboard. The hot coolant can cause the components to overheat and burn, producing smoke or steam blown through the AC vents. A heater core failure can also cause a sweet smell in the car, indicating a coolant leak. 

What Should You Do if Smoke Comes From the AC Vent When Driving?

If smoke comes through your AC vents, you must safely pull over and switch the engine off, remove the key from the ignition, and exit the car. Wait for the smoke to stop through the dashboard vents before entering the vehicle again. 

If you get back into the car, ensure all internal electrics, blowers, etc., are switched off, and turn the ignition on. If smoke starts to come through the vents again, have a recovery company collect the vehicle; do not attempt to drive. 

However, if the smoke does not continue to come out of the vents, you may be able to recontinue your journey if you feel it is safe to do so. If the smoke continues again shortly into your journey, pull over and have the vehicle recovered; it is not worth the risk!

What Are the Risks of Driving With Smoke Coming Out of the AC Vents?

The significant risk of driving with smoke coming through the AC vents is if there is a fire behind the dashboard. Fire will quickly consume a car’s cabin, and the inhalation of smoke can put you and the occupants in a nasty situation. 

When driving, you cannot see what is behind the dashboard, causing the smoke to come through the AC vents, so you should assume the worst until it is checked. 

Final Thoughts

If you experience smoke coming from your car’s AC vents, it can be dangerous, and taking immediate action is essential. Smoke from the AC vents doesn’t necessarily mean that the AC is to blame; many electronic components sit behind a dashboard that can fail and produce smoke. 

There are several potential reasons for smoke coming out of the AC vents, which you have now read about in this article. Identifying the problem and taking the necessary steps to fix it promptly to avoid any potential fire risks is essential.

My name is Tom although my friends call me Tommy. Messing around with cars and bikes has always been a hobby of mine even from a young age. So I made it my day job 17 years ago. I am a fully qualified mechanic as you would expect. I've worked in all different areas of the motor trade, valeting, panel beating, engine repairs, I'm sure you get the idea. I enjoy sharing my wealth of knowledge and experience with others, which is the reason I spend a lot of time here writing for this website.

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