Cleaning the air filter in your air conditioning unit is the single most impactful maintenance task you can do yourself. It takes 10 minutes, requires no tools, and directly affects the system’s cooling performance, energy efficiency and lifespan. Here is exactly how to do it.
How Often Should You Clean the Filter?
During periods of regular use, clean the filter every 4-6 weeks. If the system is used daily in summer, monthly cleaning is appropriate. During winter when the system is used less frequently, cleaning every 2-3 months is sufficient. Some units have a filter indicator light that illuminates when cleaning is recommended — this is a useful reminder but should not be the only trigger.
If you have pets, or if the installation is in a dusty environment (near a building site, in a workshop), clean more frequently — every 2-3 weeks during heavy use.
Step by Step — How to Clean the Filter
Step 1 — Switch off the system. Use the remote control to turn the system off, then switch off at the wall isolator switch. Do not attempt to remove filters while the unit is running.
Step 2 — Open the front panel. On virtually all wall-mounted split systems, the front panel hinges upward — lift it from the bottom edge and it will hinge up, held by clips or hinges. On some units, the panel clips off completely rather than hinging. Refer to your user manual if you are unsure of the opening mechanism for your specific model.
Step 3 — Remove the filter(s). The filter(s) are visible behind the front panel, sitting in front of the evaporator coil. They typically slide or lift out — the direction varies by model but is usually obvious once the panel is open. There may be one or two filters depending on the unit width.
Step 4 — Check the filter condition. Hold the filter up to the light. A clean filter allows light through clearly. A lightly loaded filter allows some light through. A heavily blocked filter appears dark grey or brown and lets very little light through. Even lightly loaded filters should be cleaned — do not wait until the filter is completely blocked.
Step 5 — Clean the filter. For most filters, gently vacuum the surface first using the brush attachment to remove loose dust. Then rinse under lukewarm running water from the inside face (the face that was away from the coil) through to the outside face — this pushes dirt back the way it came in. Do not use hot water, detergent or brush aggressively — filters are fragile.
Step 6 — Allow to dry completely. This is critical. Refitting a wet filter into the unit introduces moisture that can encourage mould growth on the evaporator coil. Leave the filter in a warm, dry location for at least 30-60 minutes before refitting — or use a cool hair dryer to speed up drying if needed.
Step 7 — Refit and restart. Slide or clip the filter back into position, close the front panel, and switch the unit back on at the isolator. Run in fan-only mode for 5 minutes to check normal operation before switching to cooling mode.
What a Blocked Filter Does
A heavily blocked filter restricts airflow over the evaporator coil. This causes the coil surface temperature to drop below the dew point of the room air — ice begins to form on the coil. The unit may appear to be running normally but delivers very little cooling, or the airflow from the unit reduces to almost nothing as the coil becomes encased in ice. When the system is eventually switched off, the ice melts and can overflow the drain pan, causing water damage. Regular filter cleaning prevents all of this.
What Only a Professional Can Clean
The evaporator coil behind the filter accumulates a layer of fine dust and biological matter that the filter does not catch. This requires specialist cleaning agents and techniques — it is part of our annual service and should not be attempted without the correct equipment. Call 07833 053749 or book an annual service.