A musty smell is emitting from the A/C vents. What might be the cause?

The presence of a musty smell coming from the A/C vents is often indicative of bacterial mold growth, particularly on the evaporator core. The evaporator core is a critical component of the vehicle’s air conditioning system, where moisture can accumulate. When humidity levels are high, or if the A/C system isn't regularly maintained, water can condense on the evaporator. Over time, this moisture can create an ideal environment for mold and bacteria to thrive, leading to unpleasant odors when the A/C is in operation.

Eliminating the source of moisture, such as improving drainage and ensuring that the evaporator is clean, is essential for managing odors related to mold. This approach effectively addresses the root cause of the musty smell, rather than simply masking the odor with air fresheners or other temporary solutions.

The other options relate to different issues: a recirculation door stuck in the outside air position would not typically result in a musty smell, low refrigerant levels mostly affect cooling efficiency rather than causing odors, and a blocked cabin air filter can restrict airflow and lead to discomfort, but it is less likely to directly cause a musty smell compared to mold on the evaporator.