Black mold can grow in any indoor environment, including air conditioners. Black mold starts when fungus spores are released indoors through the heating and cooling systems. When black mold is found in an air conditioner, it is usually because of a leak or malfunctioning HVAC system. Heat and moisture can cause molds to grow inside air conditioners. The humidity level in the home can also cause molds to thrive inside the air conditioner. Black mold can cause severe health problems if not removed from the air conditioning system. It can also cause damage to the AC unit, which will require a costly repair or replacement. Spray the mixture on the moldy areas. Let it sit for 10-15 minutes, then wipe it away with a paper towel. more info