The air that comes out the car air conditioning vents has mildew odor.
Car Problem Diagnosis
When an air has mildew odor comes out the car air conditioning vents this indicates that the car air conditioning system has a drain pan problem. The evaporator drain pan is not draining properly and the reason is that there is clog somewhere the drain hose.
Evaporator is the main component of the car air conditioning system which makes the air that comes out the vents to become cold, the process is that when the car a/c unit is turned on, the air that is blown from the blower passes through the fins of the evaporator once it passed the evaporator it becomes cold until it comes out the a/c vents and circulate inside the car cabin.
During the process especially on hot and humid days, moisture is formed on the evaporator and drips down to the evaporator drain pan, the moisture will then pass through a hose all the way to the streets. When the drain pan does not drain because of clogging, the moisture will get trapped inside the drain pan, when this happens an algae-like organism starts to grow, this algae produce mildew odor that is carried out by the air to the a/c vents which the driver and the passenger smells.
Possible Cause of Mildew Odor in an Air conditioning
Clogged Evaporator Drain Pan
All About Auto Recommendation
Locate the car a/c drain pan hose. Usually it is located under the vehicle. Remove any clog or debris that is located from the start of hose end, all the way up to the base of the drain pan, if you are not familiar with this kind of works seek an assistance of a reputable auto repair shop specialized in car air conditioning repair. Once the clogged was removed from the hose, it will take about a couple of days before mildew odor that comes out the a/c vents will completely be gone.