What Causes the Foul Smell When Using the Car Air Conditioner in External Circulation Mode?
2 Answers
If there is an unpleasant odor when using the car's external air circulation, a short-term smell might be due to external air pollutants, and you can simply turn off the external circulation. However, if the odor persists for a long time, it could be caused by mold or foreign objects in the air intake ducts or a dirty cabin air filter, which may require replacement. Here are some additional details: 1. Precautions: Upon entering the car, you should open the windows or activate the external circulation ventilation system to introduce fresh air. Avoid driving for extended periods with closed windows and doors, and never sleep or rest for long durations in a sealed car. 2. Solutions: If the air conditioner hasn't been used for very long and only has dust on the panel or vents, a simple wipe-down may suffice. Opening the panel, removing the filter, and rinsing it with water can often resolve minor odor issues.
I always noticed a musty smell when using the air conditioning on my car's external circulation mode. Later, I figured out it was due to a dirty air filter accumulating dust and a damp evaporator growing mold. Running it for a while even made me sneeze—so annoying! A friend helped me check, and replacing the filter immediately improved things. But the root cause was the evaporator—moisture not drying properly after long-term AC use led to bacterial growth and foul odors. Don't ignore weird smells in your car—they pollute the air and affect health, especially for allergy-prone people. I also learned a trick: clean the filter regularly, replace it yearly, and blast hot air for a few minutes before parking to keep the system dry. Now, the smell is much better.
