The floor is being cooled by the AC so that it is below the dewpoint temperature. When the humidity is high, condensation will form. You can solve this by adding insulation between the main duct and the floor.

Thanks, I’ll give it a try...

A Malfunctioning AC Unit Can Cause Mold Growth.

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A properly working air conditioner also works as a dehumidifier for your home. It pulls excess moisture from the air and drains it outside of the home. When your AC has a blocked drainage tube it can cause water to leak inside which can lead to mold growth when not noticed or repaired quickly.

Another way your air conditioner can fail to dehumidify your home is when it has a lack of refrigerant due to a leak. The evaporator coil can freeze over and your home will not cool down as it should. Unwanted moisture will remain inside as the airflow over the coil slows or ceases.

Preventing Mold Growth Due to Air Conditioner Failure.

Regular Maintenance. Prevent mold and mildew damage before it starts by keeping your AC unit professionally maintained. This means scheduling preventative maintenance with your HVAC company every year to ensure your air conditioner is running smoothly and efficiently. Maintenance includes inspecting, cleaning, and lubricating your system as well as recharging refrigerant to the proper levels.

Proper Air Conditioner Installation in Greensboro. When your air conditioning unit is first installed it must be done correctly. Improper installation of the system or the ductwork can cause problems with humidity and indoor moisture control.