Mold in an AC unit

Air handlers are damp by design: evaporator coils, drain pans and drain lines carry condensation, and duct liners stay cool. If a pan is clogged, a drain line is blocked, or a porous liner is wet, mold can grow. Florida DOH says to check around air handling units for standing water and routinely inspect coils, liner surfaces, drain pans and drain lines. If you know or suspect the system is contaminated, do not run it; it can spread mold through the building.

EPA says HVAC mold work should be done only by professionals experienced with these systems. The system is turned off, intakes and supply vents are sealed with plastic and tape, negative pressure is maintained, contaminated porous material is bagged and removed, and cleanable surfaces are HEPA vacuumed or damp wiped and dried promptly. If insulated ducts or duct lining are wet or moldy, they cannot be cleaned effectively and should be removed and replaced. No biocide is approved for lined ductwork.

Anywhere cooling equipment creates condensation, mold has a chance if the water does not drain or the surface stays wet. That includes AC closets, evaporator coils, drain pans, drain lines, and the liners and vents of mini-split and ducted systems. Florida DOH says to check around air handling units for standing water and routinely inspect coils, liners, drain pans and drain lines. Captured search data shows closets, vents, mini-splits and AC systems are common homeowner problem spots.