Car air filter: what it does and how to change one in the ventilation system

What is a car cabin air filter and how can you change it_2

Are your car’s heating and ventilation unit struggling to pump out a good flow of air? Is the air that does come into your car a bit whiffy? Or have you found yourself suffering more allergies or hay fever symptoms when behind the wheel?

If any of these scenarios sound familiar, there’s a good chance the culprit is your car’s air filter. But we’re not talking about the filter that cleans the air being fed into the engine. This is the filter that forms part of the car’s cabin ventilation system.

Technically known as the heating, ventilation and air-conditioning system – HVAC for short – this is the one part of the car most drivers take for granted. But from time to time, it requires routine maintenance. And at the heart of the system is a filter that removes pollen, dust and debris.

Changing the cabin air filter can literally breathe new life into a car’s ventilation system. Here’s how you can do it yourself. But if you’d rather leave it to an expert, we explain how to check a car manufacturer’s recommended replacement times for a cabin air filter.

When did cars start using cabin filters?

Filters for the ventilation system became the common place from 2000. Before then, it was usually luxury cars or those with an optional air-conditioning system that featured a filter. If you have an old car, you’ll know it lacks a filter because the ventilation system will occasionally blow in bits of leaves and dust.

How do they work?

All the air channelled through a car’s ventilation or air-conditioning system is passed through a filter before it reaches the cabin. Denso, a manufacturer of filters for car makers, says the most common type of cabin or pollen filter is typically made from five layers of fleece-like material. This means it can trap particles as small as 0.001 microns. That’s tiny; a human hair is typically up to 100 microns thick.

Like vacuum cleaners, many of the latest cars feature filters with carbon (charcoal) filters. These are claimed to be ultra effective at capturing minute particles and can prevent the build-up of bacteria and fungus.

When does a cabin air filter need changing?

What is a car cabin air filter and how can you change it

Different car makers may call it different things: cabin filter, microfilter or pollen filter. They also recommend different intervals for how often a cabin filter should be changed. But the one thing they agree on is it’s a job that needs to be done.

The UK’s most popular car maker, Ford, says that the cabin filter of a 2016 Focus family hatchback needs changing every 15,000 to 20,000 miles. However, it adds that this could be done more frequently if the driver (or any passengers) suffer from allergies, or if the car is used in dusty environments, such as building sites or dirt roads.

By contrast, BMW recommends that owners have the pollen filter changed every time their car requires an engine oil change. The timing of this varies according to how the vehicle is being used, as modern BMWs feature variable servicing intervals.

Is it easy to change a cabin air filter yourself?

The job of changing a pollen filter is only as easy as the car manufacturer makes it. The vehicle handbook should show its location, and you can order the part online, using the vehicle registration or chassis number to verify that it’s compatible.

Some models have been designed to be easily accessible, with the filter hidden behind the glove box. Depress a couple of catches and the glove box drops out of the way, revealing the filter. It should slide out on a tray and can be removed and replaced using just your hands. However, some cars have them hidden away in the engine bay. Tools are then required to get at them. In this case, any local garage will be able to remove and replace the part for you.

How much is a cabin air filter?

Taking the Ford Focus 1.0 petrol as an example of a popular family car, the price of filters available ranges from £5 to £25. Someone buying a pollen filter for a BMW 320d could expect to pay between £20 and £55, depending on whether or not they wanted a standard fleece filter or carbon-based part.

If you’re unsure of the condition of your car, book a vehicle service today. With the use of our quick, easy and free online booking tool, you can compare the price, distance and reviews of thousands of garages.

James Mills

James is a motoring journalist and former magazine editor at BBC Top Gear and Auto Express. He has scooped, reported on and reviewed most new cars of the past 20 years, and currently contributes to the Driving section of The Sunday Times.

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