Mold is common in environments that have dirt dampness and darkness.
Mold in air handler insulation.
You could also use an insulating hvac paint they use on ducts.
In some cases the air handlers simply are not insulated well enough in areas.
Simply put add more insulation.
Mold spores naturally traveling in the air attach to damp areas then begin to grow.
Air conditioner air handler rust condensate leaks wet insulation mold hazards leaks in the air handler can cause rust damage and may invite mold contamination in the ahu or in the hvac system ductwork.
Wear rubber gloves since bleach.
The outside of ducts more often than inside.
Unfortunately for homeowners black mold also loves air vents where spores are naturally circulated.
How to remove mold from an air handler.
Leaks out of the air handler can also damage surrounding building components such as drywall or insulation.
Mix 1 quart of liquid chlorine bleach with 3 quarts of warm water and add 1 3 cup of powdered detergent.
The insulation in air handler in my previous home became covered with mold.
It turned out that the system have a refrigerant leak and the leak meant the system was running almost continuously and producing a lot of condensate.
Enough of that moisture was transported to the air handler to saturate the fiberglass insulation.
I often find mold on the exterior of air conditioning systems more often than the interior.
Wear a respirator and goggles to prevent mold spores from interfering with your breathing or vision.