Any burning smell from your car’s air-con causes drivers to worry about whether their car is safe and will catch fire.
This article will explore the causes, whether they are dangerous, and the costs of putting them right.
In brief though
A burning rubber smell entering through your air con indicates either loose hoses rubbing against the engine, a burning plastic smell means electrical components are overheating, and a burning oil smell indicates an oil leak.
As you see, the smell isn’t always AC-related but originates from the engine area before being pumped into the car cabin through the vents.
Let’s group the smells into three distinct categories. These are the main ways that people who smell burning describe them.
- Burning rubber
- Burning plastic
- Burning oil
BURNING CAR AIRCON RUBBER SMELL
The AC compressor is faulty.
You’ll find your car’s AC compressor near the front of the engine with the rest of the belt-driven parts.
The aircon compressor is powered by a belt that attaches to the engine. It’ll turn millions of times in its lifetime but can become frayed and brittle near the end of its life. It can come into contact with the engine when it gets to this state and burns.
A more common problem with the air compressor is when the clutch becomes stuck and won’t allow the belt to turn. This can cause friction and give off a burning smell too.
Belt pulleys, when working correctly, keep the belt tight and running accurately to the crank and back to the compressor. If this is broken or misaligned, it will often cause the belt to rub against metal too.
All faults connected to the AC compressor can give off a rubber-burning smell, which can work their way into the car cabin through the vents.
How to fix this
You won’t need many tools to change an AC belt or replace a pulley, but if the fault is with the compressor clutch, you’ll need to get inside the clutch itself as it’s housed there.
Most people will take their car to the car shop if they suspect the compressor clutch is defective. Do it early, though, as the clutch pulley can often be replaced. If left too long, the whole compressor can be damaged beyond repair.
An AC compressor clutch costs between $24 and $100 for the part and between $150 and $250 in labor. Expect to pay a total price of between $175 and $350.
A brand new aircon compressor costs from $700 to $1,200, depending on the make and model of the car you drive.
Rubber Hoses are Loose
There are meters of rubber hosing under the hood of your car. If one becomes disconnected, it can contact a hot engine or exhaust system. It won’t take long for it to start smoking, and the rubber smell will find its way into your car’s cabin when the vents are open and the aircon is on.
How to fix this.
You’ll need to open the hood and have a good look inside the engine bay. You may see smoke – but not always – coming from the offending rubber hose. Go around all the hoses and scrutinize the connections. Are they loose? Can you hear hissing?
If they’re not in contact with the engine now you’ve stopped, could they touch it when the engine is vibrating as you’re driving? Can you see burn marks on any of the hoses?
If you find any damaged hoses, replace them and ensure they are more securely clipped in place. If needed, buy new hose clips too.
This is a job that you may feel you can do yourself. Rubber hoses are very cheap, and the clips cost only a few dollars.
A mechanic shouldn’t charge you more than $100, including parts and labor, to put things right if you’d rather a professional make the repair.
Burning Out Clutch (Manual cars only)
All smells from under the hood will find their way into your cabin through the vents. Some, though, you’ll only smell in certain circumstances.
A burning clutch – not the air compressor clutch – occurs more often when driving slowly in a line of traffic, especially if you are in a line on an incline.
Every time you push the clutch pedal in these circumstances and engage a gear, your clutch is asked to work more often and harder. This can cause a burning smell if your clutch is near the end of its life.
The smell would disperse into the air outside the car if you were driving at any speed, but when stationary, it will find its way into the vents.
Fitting a new clutch is normally the job of experienced DIY mechanics or professionals.
A new clutch will cost between $200 and $400 for the part and another $200 to $300 for the fitting. The price difference depends on the make and model of the car and the hourly labor rate charge.
BURNING PLASTIC SMELL
There are two causes of your car’s AC smelling like burning plastic.
A build-up of dust particles
If you’ve just turned your AC on for the first time in a few months, the smell might be caused by a build-up of dust. Strange to think dust could smell like burning plastic, but some people report this.
If dust is the cause, it will only last a very short time before fading. If the smell remains for more than 30 seconds, it’s unlikely to be a dust issue.
Check the cabin filter as if it’s blocked or badly fitted it may let dust and debris into the vents where it’ll congregate and let off a burning smell especially after being left sitting over the winter and then used for the first time.
Your car’s systems run off electric power from the alternator and the battery. Occasionally the wiring going to and from the electrical components shorts.
This means the circuit is broken, and wires or the electrical motor or valve to which the power runs can get heated.
Sometimes the smell can be powerful and overpowering. Occasionally, the fault can lead to electrical fires, which will produce toxic fumes.
If you smell burning plastic in your cabin, it’s time to get your car inspected by a mechanic. It could be straightforward to fix, like having a new section of wire fitted.
However, the burning smell could be an early warning signal that your car suffers from a major electrical problem. Have a check under the hood and look for singed wires. This is a sign of too much current passing through the system or bad grounding.
It’s difficult to estimate the repair cost as it depends on the part – if any – that needs replacing and the number of labor hours needed to fix it.
It has been known for plastic bags to catch on the exhaust and then melt there causing a burning plastic smell. This is more likely in the cabin when the air con is on if the bag is caught neat the exhaust manifold connected to the engine under the hood.
Your car’s alternator provides all the electrical energy your car needs when the engine is running. It’s a big undertaking, and when they go wrong, they get hot and can give off a burning smell. Often the ECU will put the alternator into limp mode when it gets too hot.
The alternator serpentine belt could be loose and rubbing if the smell is like burning rubber.
If it’s a plastic burning smell, it is more likely caused by the bearings inside the alternator or the cables going to your battery from the alternator. You’ll probably hear a grinding noise too.
How to fix this.
If you’ve discounted a dust build-up and damaged wires or shorting out, it could be the alternator is overheating.
As we’ve discussed, any burning smell in the engine area will find its way through the AC system and into the cabin.
A mechanic can diagnose an alternator fault by running a few tests with a multimeter.
An alternator can often be rebuilt, but sometimes a car shop will send them away to a specialist.
As a general rule brand new alternator will cost from $175 to $350. Labor costs range from $200 to $400 so expect to pay between $375 and $750 in total.
Of course, your car’s AC isn’t powered by the engine or the oil within it, so why is burning oil on the list, you may ask?
As you’ve seen, most of the smells coming through the vents are not caused by the AC system. The AC picks up the smells from other areas of your car and transports them into your cabin.
Diagnosing burning oil is the easiest of the three smells you may encounter. It can sometimes get compared to a gas smell, but oil smells less sweet.
Open the hood and have a look inside. Have you or a mechanic just changed or topped up the oil?
The car’s engine gets very hot, and just a small amount of oil on it can cause it to smoke and burn.
Other areas to look at are the oil filter and the gasket, which keeps the top half, and the bottom half of your engine secured tightly. Is there any leaking here?
Oil can drip onto the exhaust manifold of your car as well.
Other fluids under the hood could also give a burning oil smell.
If you can’t see any obvious oil leak, check the transmission fluid reservoir – not manual – the brake fluid and power steering fluid too. If hot, these will smell like burning oil.
How To fix
Unfortunately, the repair can be as simple as a loose hose allowing fluid to escape to a more involved and costly job such as replacing a gasket cover. The cost of repair will vary greatly too.
The burning smell from your car’s AC is unlikely to be caused by your car’s AC. The AC transports the burning smell into your cabin.
The burning smells are grouped closely into Plastic, Oil (or fluid), and Rubber, so it’s fairly easy to discount most of the causes before you even start diagnosis.
Always get a mechanic to check over your car as soon as you can. A burning smell is never a good smell. Your car has oil, gasoline, and electrical cables galore running through it.
The sooner it’s diagnosed and fixed, the safer you’ll be and the cheaper the repair cost.
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