What are the signs of mold in your AC or HVAC system?

The most commonly reported sign is a musty, earthy odor that appears or intensifies when the air conditioning kicks on. Because the HVAC system moves air throughout the home, an odor that tracks with the system cycling is a classic clue that the source is somewhere in the equipment or ducts.

Look at the supply vents and registers for dark speckling or staining on and around the grille. Around the air handler, check the drain pan, the area near the evaporator coil, and any insulation for dark growth or water staining. These are cold, damp spots where condensation collects — exactly the conditions mold needs.

Not every dark mark is mold, and you should not disturb suspected growth. But visible speckling at multiple vents, combined with an odor, is worth a professional look.

Air conditioning works by cooling air below its dew point, which pulls water out of it. That water collects on the coil and in the drain pan and is supposed to drain away. When a condensate line clogs, a pan overflows, a system is oversized and short-cycles without dehumidifying well, or ducts sweat, you get sustained moisture in a dark, enclosed space — an ideal setting for growth in Florida's humidity.

Some people report that a musty odor or the way they feel at home eases when they spend time away and returns when they are back. That is a commonly described pattern, not a diagnosis — how a person feels is a medical question for a physician, not something an inspection determines.

What an inspection can do is check the building side: assess the air handler, drain pan, and condensate line, measure moisture and humidity, and use thermal imaging to find damp areas. If mold is confirmed in the system, the fix is to correct the moisture source and have the affected components properly cleaned or replaced.