Maintenance
How to clean your air conditioner filter
It takes about ten minutes with a vacuum cleaner and a tap. No other job you can do on an air conditioner without a licence makes as much difference. A surprising share of the breakdown calls we go to in January come down to a filter nobody has touched since the system went in.
6 min read
The short version
What the filter does
The filter mainly protects the coil behind it. That coil is a dense block of aluminium fins with very little space between them. Once dust gets into it, a vacuum will not get it out. It needs chemicals, water and the unit stripped down.
So the filter works as a sacrificial layer. It catches the dust so the coil does not. A choked filter is still doing that job, but leave it long enough and dust starts getting past it into the coil. That is a far bigger clean than ten minutes at the tap.
On a wall-mounted split system the filters sit behind the front panel. On a ducted system one large filter sits behind the return air grille.
Cleaning a split system filter
The wall-mounted indoor unit in a bedroom or living room. Almost every brand works the same way.
- 1
Switch it off at the wall
The remote is not enough. Use the isolator or the wall switch so the fan cannot start while your hands are inside the unit.
- 2
Lift the front panel
It hinges upward from the bottom edge and usually stays open by itself. If it will not move, look for a clip at each end instead of pulling harder.
- 3
Slide the filters out
You will find two mesh panels in slots. Push each one up slightly to release it, then draw it down and out. Take a photo first if you want to be sure which way round they go back.
- 4
Vacuum the loose dust off first
Use a soft brush head over the dirty face. Doing this before any water touches the filter stops dry dust turning into wet paste.
- 5
Rinse from the clean side
Run lukewarm water through the back of the filter so it pushes the dust out the way it came in. A kitchen filter can get greasy, so add a little dishwashing liquid to warm water. Avoid hot water and stiff brushes because both distort the mesh.
- 6
Dry completely in the shade
A damp filter put straight back is how a system starts smelling musty. Lay them flat somewhere with a breeze and out of direct sun, which makes the plastic mesh brittle. Give it an hour or two.
- 7
Put them back and close up
Seat the filters properly in their slots, click the panel shut and switch the power back on. Never run the system with the filters out, even for a short while.
Cleaning a ducted return air filter
Same idea, bigger filter. People miss this one because they go looking at the outlet vents in each room.
- 1
Find the return air grille
Look for the biggest vent in the house, most often in a hallway ceiling. You can feel it pulling air in when the system runs.
- 2
Switch the system off, then open the grille
Most hinge down on two clips. Some use screws. Support the weight as it comes down, because a ceiling grille is heavier than it looks.
- 3
Check what type of filter it is
Washable mesh gets the same treatment as a split system filter. A pleated or paper filter is disposable, so you replace it instead of washing it. Mesh you can see through is washable. A concertina of white fabric is not.
- 4
Vacuum, rinse and dry it flat
A shower recess or a driveway is easier than a laundry sink for a filter this size. Dry it flat so it keeps its shape and give it longer than you think it needs.
- 5
Refit and latch it properly
An unlatched grille rattles and lets air bypass the filter completely.
How often to clean it
Manufacturer manuals tend to say a fortnight, which almost nobody does. These are the intervals we recommend, based on what we find when we open units up.
| Situation | Interval | Why |
|---|---|---|
| Running daily through summer | Every 4 to 6 weeks | Peak run hours pull the most dust through the mesh |
| Seasonal use only | Before summer and before winter | Catches the dust that settled while it sat idle |
| Pets in the house | Every 3 to 4 weeks | Hair mats the mesh far faster than dust alone |
| Kitchen or open-plan living | Every 3 to 4 weeks | Cooking oil makes the dust sticky so it clings to the mesh |
| Asthma or allergies in the house | Every 3 weeks, year round | The filter is protecting people as well as the coil here |
If a filter still looks clean at these intervals, stretch them out. The filter itself is the best guide you have.
What a clean filter will not fix
Weak airflow with clean filters means the problem is further in. A dirty indoor coil, a blocked outdoor unit, a slow fan or a refrigerant leak are the usual candidates. None of those are DIY and two of them legally need a licence to touch. If the system is also leaking water, start there.
A smell that survives a filter clean usually means growth on the coil fins or in the tray below them. The unit needs opening up and chemically cleaning. Our air conditioning repair and service page covers what a full service takes in.
Skip the coil cleaner spray
Common questions
- How often should I clean my air conditioner filter?
- Every four to six weeks while the system runs daily. If it only runs seasonally, clean it before summer and before winter. Do it more often with pets in the house, anyone with asthma or a unit near the kitchen.
- Can I wash an air conditioner filter with water?
- Yes, if it is a reusable mesh filter. Most split systems and many ducted return grilles use them. Run lukewarm water through it from the clean side so the dust comes back out the way it went in. Paper or pleated filters are disposable, so replace those instead.
- What happens if you never clean your air conditioner filter?
- Airflow drops, so the room takes longer to cool and the system runs longer to get there. Eventually the coil runs cold enough to ice up. When the ice melts it overruns the drain tray and the unit leaks. Dust that gets past a loaded filter also settles on the coil, which is a much harder clean.
- Is cleaning the filter the same as a service?
- No. Cleaning the filter is housekeeping you can do yourself. A service covers what you cannot reach or are not licensed for: coil condition, refrigerant pressures, electrical connections, the drain line and the outdoor unit. Cleaning the filter between services still makes a real difference.