Short answer: mold in a Miami AC system usually grows on the evaporator coil, in the drain pan, on the blower wheel and in the insulated supply plenum. We clean and treat those parts, remove duct liner or duct board that can't be cleaned, and fix the reason the system stays wet, which is the part a quick clean skips.
Signs the mold is in the AC
- A musty or sour smell that starts a few minutes after the system kicks on.
- Dark spotting on supply vents and the ceiling around them.
- Water in the pan under the air handler, or a stain on the closet floor.
- Allergy-type symptoms that ease when you leave the house.
Spots on a vent cover alone are often condensation dust on the grille, not a system problem. We open the air handler before we tell you either way.
Why Miami systems grow mold
An AC here spends most of the year pulling water out of the air. A typical system removes gallons a day, and every drop has to run off the coil, into the pan and out through the condensate line. Anything that slows that water down leaves a warm, wet, dusty surface in the dark, which is exactly what mold wants. The usual culprits:
- Clogged condensate lines. Algae builds up in the line, the pan overflows and the closet stays damp.
- Fan set to ON instead of AUTO. With the fan running between cooling cycles, water sitting on the coil is blown back into the house as humidity.
- Oversized units. A system that cools the house in a few minutes shuts off before it has removed much moisture, so the air feels cold and clammy.
- Leaky returns. A return that pulls air from the attic or a garage drags in hot, humid air and dust.
- Thermostat turned off while away. A closed-up house in August can climb past 70 percent indoor humidity in days.
What we do
- Inspect inside the cabinet. Coil, pan, blower, plenum and the first run of duct, with photos so you see what we see.
- Protect the house. The system is shut down, registers are sealed, and the closet or attic platform is contained when the growth is heavy.
- Clean the air handler. Coil cleaned, pan scrubbed and treated, blower wheel cleaned, cabinet interior HEPA-vacuumed.
- Deal with the ducts. Metal duct cleaned with HEPA vacuum and brushing; contaminated duct board, liner or flex duct removed and replaced by a licensed HVAC contractor where needed.
- Fix the drainage. Condensate line cleared and the pan's float switch checked, so an overflow shuts the system off rather than flooding the closet.
- Check the rooms. Closet walls, ceilings near the supply vents and the return wall get a moisture check too.
Keeping it from coming back
Keep the fan on AUTO, change filters on schedule, and flush the condensate line every few months; a cup of white vinegar poured into the access port is the standard trick. When you leave the house for a while in summer, set the thermostat around 78 rather than turning the system off. A plug-in hygrometer from a hardware store tells you whether indoor humidity is staying under 60 percent, which is the number that matters.
Typical prices
| Job | Estimate | What it covers |
|---|---|---|
| Evaporator coil cleaned in place | $100–$400 | Coil cleaned and treated without removal |
| Coil pulled and cleaned | $400–$700 | When growth is heavy or the coil is packed with debris |
| Whole-house duct cleaning | $300–$600 | About 1,500 sq ft home, metal or cleanable duct |
| AC and duct system mold remediation | $2,000–$10,000 | Air handler, plenums and duct runs, contained |
| Drain pan and condensate line | Priced on inspection | Depends on pan condition and access |
| Duct board or flex duct replacement | Quoted with your HVAC contractor | Porous duct that can't be cleaned |
Ranges, not quotes. System size, duct type and whether anything needs replacing move AC mold work more than anything else, so treat these as a starting point until we've opened your air handler. More in the price guide.
Related services
Questions
Can moldy ductwork be cleaned, or does it have to be replaced?
Sheet-metal duct can be cleaned. Fiberglass duct board and the lined inside of flex duct generally cannot; the EPA's guidance is that wet or moldy insulation in ducts should be removed and replaced. We tell you which you have before we quote.
Will spraying a fogger through the vents fix it?
No. Fogging puts a chemical on top of the growth and leaves the growth, and the moisture feeding it, where they were. The smell often comes back within weeks.
Do you replace AC units?
No. We are a remediation company. If the air handler is past cleaning, we say so in writing and you call your HVAC contractor; we can work around their schedule.
Last updated October 8, 2026