What Causes the Odor When Turning on the Car Air Conditioning?

[DelMaya]

Car air conditioning emits an odor due to mold growth in the evaporator box and ventilation ducts. The functions of car air conditioning include: 1. Achieving a cooling effect through the continuous cycle and transformation of refrigerant; 2. Drawing in fresh external air for ventilation and air exchange to prevent windshield fogging; 3. Utilizing the engine coolant, waste heat, or heat generated by a burner as a heating source, which is then warmed by the heater and blown into the car by the blower to raise the temperature for heating purposes; 4. Removing dust, odors, smoke, and toxic gases from the car's interior to freshen the air, as well as humidifying the air to increase its relative humidity.

[AlexanderAnn]

I totally relate to the weird smell when turning on the car AC—it's likely due to mold growing on your AC system's evaporator. The condensation left after using the AC, if not fully dried, becomes a breeding ground for bacteria, causing that musty odor. My advice: Turn off the AC a few minutes before parking and let the fan run to dry out the ducts, which significantly reduces mold buildup. Also, remember to regularly clean or replace the cabin air filter, as accumulated dust can also create odors. If the smell persists, try using a specialized AC cleaner spray on the air intake—it's an easy DIY fix. But for strong odors, it's safer to have a professional perform a thorough disassembly and cleaning. Daily preventive habits are better than cure.

[VanRose]

The main cause of unpleasant odors from the air conditioning is often the growth of mold inside the system, especially in areas where condensation accumulates on the evaporator surface. The damp environment promotes mold growth, and this is more likely to happen when the air conditioning is used frequently in summer. Another possible reason could be a dirty air filter that blocks airflow. When I checked my own car, I found that the filter had not been changed for six months, leading to dust buildup and foul odors. It is recommended to replace the filter every spring and, before parking, turn off the AC and run the fan for 10 minutes to help dry the system, preventing it from becoming a breeding ground for bacteria. Simple maintenance can save you a lot of trouble.

[RiverDella]

That odor is mostly caused by mold in the air conditioning system, which may not be good for health. Inhaling mold spores can irritate the respiratory tract. The key issue is the system being damp and not properly dried out, so regular cleaning of the evaporator and ducts is crucial. You can use disinfectant sprays or seek professional treatment from a technician to prevent allergy problems.