A:Answer Here's a very simple way to test/confirm that the VOC sensor is functioning, without having to power cycle the unit (to watch the start up sensor light sequence). Place 5300B in Auto mode operation, in a room where normal ambient air is assessed by the 5300B VOC sensor to be Green. Take a 4in x 4in clean cotton cloth square & spritz it w/ 70% isopropol alcohol until it is damp to the touch. Place this damp cloth square within 4ft of the 5300B. If the 5300B's VOC sensor is working, Auto mode will quickly speed up and the senor light will jump from Green to Red. As an added bonus, you can time how long it takes for the 5300B in Auto mode to clear the room air back to Green. If/when the VOC sensor is functioning, this test will trigger it every time.