In this video Derek Cole explains why residential air‑conditioning systems can develop a damp, musty odor when they are first turned on. He describes the basic refrigeration cycle: warm indoor air passes over a cold coil containing refrigerant, which removes heat and causes moisture in the air to condense. The condensate drips into a drain pan and then out through a drain line. If the pan does not drain properly, standing water creates a dark, damp environment where bacteria, mold and other microbes can grow. This microbial growth produces the characteristic musty smell. Cole recommends installing a UV‑light coil scrubber that shines ultraviolet light on the indoor coil; UV kills the microbes, preventing growth and eliminating the odor. He illustrates the principle by comparing it to sunlight drying a damp mat, emphasizing that the same UV energy can be used inside the HVAC system to keep it clean.
Chapters
In air conditioning, you have to remove moisture to get humidity out of there. So, uh, air conditioning is all about removing heat, right? So you're taking heat out of the air, it's going over a cold coil which has refrigerant in it, and then it's coming back out cooler air than what came in. So the byproduct of that is water. So that's why you have drain lines, that's why you see water dripping outside. So what will happen is when you have that hot air going across that cold coil, you get condensation, and that's going to drip down to the drain pan. Well, if that drain pan is not draining or something is the matter, things will start growing in that drain pan because you have cold water sitting in a damp, dark spot. So the thing that happens is growth, right? So even the most— the strongest bacteria in the world lasts 24 hours. So If it's not in the air, or if it's a bug, or it's a virus, or whatever it is, it's going to die and it's going to sit at the bottom in that drain pan for a period of time. So you start getting— the first time you turn on your heat or your air conditioning, especially, you get that kind of damp, musty, moldy kind of smell. Um, there's like all kinds of mold, so we don't call it mold, call it growth. So the way to prevent that from happening is to introduce UV into that system somehow. Now we do it here with the coil scrubber, which shines on the indoor coil, has the UV power, so nothing can grow in UV. If you want to prove that point, uh, everybody at home has that mat at the front or back of the house that has the mildew and it's kind of wet and it's kind of damp. Take that mat, stick it out in the middle of the yard in the sunshine for a period of time, and that will be clean and dry because nothing can grow when UV is present, right? So in the indoor air environment, in the air handler, that is not present. So we have to make it present with UV light. UV light will solve that problem. So the same power of the sun, the same energy that holds, we can bring into your system, and that'll stop that damp, dusty musty smell.
