This is often in the evaporator coils or the drain pan, but can also be in the ducts themselves or in the sound dampening foam used at part connections. To help, some automakers, such as Ford, Honda, and others, began installing filters to prevent ventilation system contamination. Avoid AC-MAX, which circulates unfiltered passenger compartment air back into the AC unit, defeating the purpose of the filter. Filters only last so long before mold spores penetrate and grow on the inside face of the filter. If you begin having problems, probably after 10-12 months of use, change this filter.
Molds are necessary for plant life.
Other molds can harm plants and contribute to root rot, and others exist in soil in symbiotic relationships to aid in the growth of the plant. Because molds often grow well only on specific plants, some healthy houseplants can cause severe allergies, and others cause none. Wherever there is plant life there is mold. An increase in allergy symptoms is often noticed just after watering plants. Usually, house plants are NOT a serious contributor to the symptoms of my patients.