Disconnect the power cord, remove the air cleaner from your heating/cooling system, and take the unit outside. Undo the two clips holding the air cleaner together and open like a book on a flat surface, removing the center screen. Notice that if the collector pads have changed from a snow-white color to a dirty gray or black, it is time to remove and discard the two collector pads.
Brush any heavy dust accumulation from the outside screens with a soft cloth or the old pads. Insert two clean pads, making sure that they are well centered in the frame. Replace the center screen, close the air cleaner, and reposition the two clips, which hold the air cleaner together. Check that the two pads did not shift as you closed the air cleaner leaving gaps between the media pads and the edge of the air cleaner frame.
Replace the air cleaner in you heating/cooling system, reconnect the power cord, and observe that the light is "ON".