For AC17xx, AC29xx, AC30xx, AC38xx, AC42xx, there is no pre-filter. When the filter cleaning alert (Figure 1) displays on the screen, clean the surface of the filter with a vacuum cleaner. When the filter replacement alert (Figure 2) displays on the screen, it's time to replace the filter. Please check your user manual to see replacement indications specific for your model.
For AC08xx, there is no pre-filter nor filter cleaning alert. Please follow the cleaning schedule and instructions on user manual to clean the surface of the filter with a wet cloth or a vacuum cleaner. When the filter replacement alert (Figure 2) displays on the screen, it's time to replace the filter. Please check your user manual to see replacement indications specific for your model.