The third step in cleaning your air conditioning system is UV light. The main purpose of UV light is to kill mold and mildew that will grow on the a/c coils. The secondary benefit is killing viruses and bacteria.

In order for UV light to work, it must be placed preferably on the down stream side of the coils. It is EXTREMELY important that the bulbs stretch all the way across the coils so both sides of the fins are in direct view of the UV bulb. This is imperative in order for the UV light to keep mold and mildew from growing on the coils.

UV light does not kill by “reflection”. Putting a small bulb that stretches halfway across the coil fins and gives off a “blue light” does not constitute a properly sized system. A single bulb system can keep the coils clean but it will take a dual bulb system to adequately kill airborne viruses and bacteria. It takes an intense light to kill the viruses and enough dwell time for the viruses passing across the bulb.

Because the typical a/c plenum does not allow for the dwell time the only way to effectively go after the viruses is to use a dual bulb system and get more UV output. It should be noted that viruses are so small they will pass through HEPA filters and this is why in “clean rooms” or surgery rooms a combination of HEPA and UV lights are used.