What Actually Happens When UV-C Light Hits Your Coil
Think of your evaporator coil like a car windshield on a humid morning. Moisture constantly condenses on its surface. But unlike your windshield, this coil sits in a dark, damp box that never sees sunlight. Over time, mold, bacteria, and biofilm build up on the coil fins — a slimy layer that restricts airflow and acts like an insulating blanket that reduces your system’s ability to cool or heat your air efficiently.
UV-C light at the 253.7nm wavelength disrupts the DNA of these microorganisms, preventing them from reproducing and eventually killing them. [Citation: 1] When a UV-C lamp is installed with direct line-of-sight to the evaporator coil and runs continuously (24/7), it creates a constant germicidal field that prevents biological growth from taking hold. [Citation: 2]
Over time, the existing biological layer dies, dries out, and is gradually washed away by condensate (the water that naturally drips off the coil during cooling cycles). This is why visible results take weeks, not hours — UV-C kills the organisms quickly, but the physical cleanup happens as the dead material decomposes and rinses away. [Citation: 3]
💡 Key Concept: Killing vs. Cleaning — Why It Takes Time
UV-C can sterilize surface microorganisms within hours. [Citation: 4] But a visibly clean coil takes longer because the dead biofilm must physically break down and wash off. Think of it like this: killing weeds in your garden is fast, but the dead weeds still need to decompose before the garden looks clean. The same principle applies to your coil.