Your indoor air is probably clean with no pollutants in it. To verify this, place a dry erase marker - or another object emitting a strong smell such as a perfumed item or food - close to the Power switch of your AP-230Ph or AP-300PHAir Purifier. If you have an AeraMax purifier it is located in the following area:
AeraMax 90/100/DX5: Place the item close to the right side of the handle on the back of your purifier. The AeraSmart Sensor is located to the right of the handle.
AeraMax 190/200/DX55/290/300/DX95: Place the item close to the Fan Speed Indicator on the right side of the machine.
The air quality sensor, located just below the Power switch, will detect the odor after a few seconds and trigger the yellow or red level of your Air Quality Indicator. If this experiment does not work, verify that the bag has been removed from around your filters and conduct the above experiment again. If this still does not work, the Air Quality sensor of the unit is probably defective. Please contact customer service.