The pollen filter on an Audi A5 is not where most people go looking for it. There is no engine bay scuttle panel to lift and no glove box to drop down. It sits above the passenger footwell, and you get to it by lying across the passenger seat and working upwards, which is why plenty of A5s are driving around on a filter that has never been changed.
The one that came out of this car was genuinely unpleasant, and that is normal for a filter that has been quietly collecting leaves, dust and damp for years. It is the only thing between the outside air and what you and your passengers breathe, and once it is saturated it stops working as a filter and starts working as a source.
The job needs no tools at all beyond your fingers. Three thumb screws, a cover, and a filter that slides out. The only part worth concentrating on is getting the new one in the right way round.
Do it before summer, not during
A blocked pollen filter shows itself as weak airflow from the vents, windows that mist and will not clear, and a musty smell when the fan comes on. Those symptoms peak when you are asking most of the system, so the sensible time to change it is before the hay fever season and before the cold damp mornings, not in the middle of either.
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Step-by-Step Guide
Get comfortable in the passenger footwell
Push the passenger seat all the way back and lie across it so you are looking up into the footwell rather than crouching outside the car. This job is entirely done above your head and being in an awkward position is the main reason people rush it and break a clip. A torch propped where it lights the underside of the dash makes a real difference.
Undo the three thumb screws holding the soft cover
There is a soft trim cover above the footwell held by thumb screws. Two are easy to spot together, and there is a third set further back that is easy to miss, which is worth knowing before you start pulling. All three undo by hand. If one is stiff, a screwdriver will start it, but they are designed to need nothing.
Lower the soft cover out of the way
With all three screws out, the cover pulls down and away. Put it somewhere it will not get stood on. Do not force it if it still feels tethered, because that means a screw is still in, almost always the one further back.
Slide the white filter cover towards the outside of the car
Behind the soft trim is a white plastic cover. It does not pull straight down and it does not unclip downwards. It slides sideways, towards the outside of the car, and then comes away. Trying to lever it off is how the tabs get broken, so if it is not moving, check you are pushing it in the right direction rather than pushing harder.
Note the shape and orientation, then pull the old filter down
Before the old filter comes out, look at it. It has a distinctive cutout at one end and it carries an airflow direction arrow. Register which way round it sits now, because that is the answer to fitting the new one correctly. Then pull it down and out. Expect it to be filthy, and expect some debris to come with it.
Clean out anything that fell into the housing
Leaves, seeds and grit collect in the housing above the filter and will drop as you remove it. Wipe or vacuum out what you can reach. It takes a moment and stops the new filter starting its life partly blocked.
Fit the new filter the right way round
Match the new filter to the old one for shape and get the cutout on the correct side, then check the airflow arrow points the same way the old one did. Feed it up into the housing and let it seat. A filter fitted backwards still fits and still filters, but it works against its own pleat design and is the sort of thing that quietly annoys you later.
Refit the white cover, then the soft trim
Push the white cover up into place, making sure it goes behind its retaining tabs, then slide it back towards the driver's side until it locks. Then slide the soft cover up underneath the hard plastic and feel for the three screw holes lining up before you start any threads. Wind all three thumb screws in by hand, and check the cover sits flush rather than sagging.
How Often the A5 Filter Should Be Changed
Once a year, or every service, is a sensible rule for a UK car. The interval that matters is not really mileage, it is time and environment, because a filter collects pollen, damp and organic debris whether the car is being driven hard or sitting on a drive under a tree.
Town cars and cars parked outside under trees load up faster. If you do a lot of miles on rural roads in summer you will fill one quicker than somebody doing the same mileage on motorways. If in doubt, take it out and look at it, since this filter costs very little and the inspection is most of the job anyway.
It is also worth knowing that this is one of the most commonly skipped items in a budget service. If your A5 has had cheap servicing and the filter looks like it has been there since the car was new, it probably has.
Standard or Activated Carbon?
A standard particulate filter catches dust, pollen and debris. An activated carbon filter does the same and additionally adsorbs odours and some exhaust gases, which is noticeable if you sit in traffic a lot or drive behind diesels on a commute.
Carbon filters cost a little more and, on some cars, restrict airflow very slightly more when new. For most A5 owners the carbon version is worth it, particularly if the reason you are changing the filter is a smell rather than weak airflow. If your complaint is purely that the vents are weak, a standard filter fitted regularly is perfectly fine.
If the Smell Survives the New Filter
A fresh filter cures most cases. When it does not, the usual culprit is the evaporator behind the dash, which sits wet and dark and grows a biofilm that smells musty the moment the fan starts. An air conditioning cleaner sprayed into the intake, or a proper evaporator treatment, deals with most of it.
The other thing to check is the drain. If the air conditioning condensate drain is blocked, water sits where it should not and the whole heater box stays damp. A wet passenger footwell carpet alongside a musty smell points firmly at this rather than at the filter you have just replaced.
Common Mistakes
- Looking in the engine bay. On the A5 the filter is in the passenger footwell, not under a scuttle panel.
- Missing the third thumb screw. Two are obvious and one sits further back. Pulling with it still in breaks trim.
- Levering the white cover downwards. It slides towards the outside of the car. Force in the wrong direction snaps the tabs.
- Not noting the old filter's orientation before removing it. The cutout and the airflow arrow are the whole answer.
- Fitting the new filter backwards. It will go in, and it will work worse than it should.
- Leaving the debris that falls out. It goes straight back into the new filter.
- Cross-threading the thumb screws. Line the holes up by feel first, then start them by hand.
