WHERE DID THAT MOLD COME FROM?

Mold and mildew is the result of liquid water coming in contact with mold spores. The spores are everywhere! In an air conditioning context, the liquid water results from airborne moisture coming in conact with a surface colder than the water vapor temperature. Remember the "sweating" of a cold glass of iced tea in the summer? The surface temperature of the glass is lower than the vapor temperature of the air, resulting in condensation. If window frames are damp, you probably have the wrong type window frame.