Why the leak shows up as a ceiling stain
Air handlers in attics sit above finished rooms. A secondary pan and a float switch are meant to catch overflow and shut the system down, but an old pan rusts, a switch gets bypassed, or the secondary drain clogs too. The first sign is often a brown ring on the ceiling under the unit or water dripping from a supply vent.
Closets and crawl spaces
An air handler in a hall closet leaks onto the subfloor and into the carpet of the next room. One in a crawl space drips onto the vapor barrier, where nobody sees it until the floor above feels soft or the house smells damp. Condensate that has sat in a pan is treated as Category 2.
Drying and keeping it from coming back
Wet ceiling drywall and insulation are checked and removed where soaked, and the joist bays are dried with air movers and a dehumidifier. An HVAC technician clears the drain and checks the pan and float switch. Energy Saver covers air conditioner maintenance, and the EPA covers humidity and indoor air.
