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Why does my car’s air conditioning smell?

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Updated 23 Nov 2020

Jason Unrau

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In warm weather, you can keep your car cool and comfortable by switching on the air conditioning.

Your car’s aircon whisks away heat and draws the moisture out of your car interior. That’s what makes it feel cooler inside your car.

If you turn on your air conditioning and a bad smell takes your breath away, you might be inclined just to go without.

What causes your aircon to smell and how can you best deal with it?

Causes of Aircon Smells


Your air conditioning dries the air in your car, but that moisture must go somewhere. Water droplets form on the evaporator core in your instrument panel, then run out of a drain tube to the ground outside.

It’s a damp environment – a perfect breeding ground for mildew.

Mildew is made up of fungal filaments. It forms on the evaporator and in the HVAC housing when there’s no airflow past it.

That mildew slowly builds up, then when you switch on the air-con, air passes over the evaporator and carries that foul smell out of the dash vents.

How do you clear up mildew on your evaporator?

There is a way to treat mildew in your heating and air conditioning system, which involves spraying a mildew and mold-killing cleaner into your cabin air intake.

The cleaner must coat the mildew well to kill it, otherwise it will return. But prevention is easier than treatment.

Keep mildew from forming in your air-con. Before you shut your engine off, turn your heater controls to draw fresh air into your car instead of recirculating the cabin air. In this way, the moisture inside your air-con system will be drawn out and expelled.

Dirty Cabin Air Filter

Many vehicles now possess a cabin air filter.

The air that’s drawn into your car’s interior for air conditioning passes through the filter, removing dust, pollen and other allergens.

When your cabin air filter gets dirty and plugged, it can trap moisture in its layers as well.

That moisture and dirt in the filter is a breeding ground for bacteria. The longer it sits, the more the bacteria spreads and festers in the filter.

When you turn the interior fan on in your vehicle, air flows through the dirty cabin air filter, causing a ripe, foul smell to emanate inside your car.

Luckily, that repulsive smell is easily remedied.

If it’s your cabin air filter that’s causing the stench from your aircon, all you need is a new cabin air filter.

On most vehicles, the filter is simple to change and won’t cost you the earth.

Now, imagine a seamless segue here...

Right. AutoGuru lets you search, compare and book from over 1,600 qualified mechanics across Australia. Boom!

Image Credit: Ferrari 458 Italia Spider - N. Palmero

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Written By

Jason Unrau

Jason is a Canadian automotive content writer with a background in the auto service industry, but he’s been hooked on cars and mechanics since childhood.

One of his first cars was an ’80 Mazda RX-7 that’s sorely missed to this day. A ’68 Ford Torino GT, a ’66 Ford Country Squire Woodie station wagon, and a ’96 Suzuki GSX-R 750 have spent time in his fleet of cars, bikes, and trucks over the past two decades.

Jason’s pride and joy is under construction – a turbocharged ’88 Mazda RX-7 convertible. Also on his resume is CASCAR official certification.