Why Does the Car AC Blow Smelly Cold Air?

[LePaul]

Foul odors from the car AC when blowing cold air may be caused by: 1. Dirty air conditioning ventilation ducts or a clogged cabin air filter. The cabin air filter should be replaced regularly, as an excessively dirty filter not only fails to function properly but also causes secondary pollution to the air entering the vehicle. To completely eliminate odors inside the car, it's essential to address the root cause. Under normal conditions, an OEM cabin air filter has a service life of one year or 30,000 kilometers. If the vehicle frequently operates in areas with poor air quality, the replacement interval should be shortened accordingly. 2. Long-term use of the AC evaporator can lead to mold growth due to moisture, resulting in unpleasant smells. Drivers should turn off the AC cooling 5 minutes before reaching their destination and switch to natural ventilation. This allows the temperature inside the AC ducts to return to normal before parking, preventing condensation due to temperature differences after turning off the engine. Keeping the AC ducts dry inhibits the growth of mold and fungi.

[EvelynAnn]

Having unpleasant odors when turning on the AC is a very common issue, mainly caused by mold and dust buildup in the air conditioning system. Take the evaporator for example - its surface temperature gets extremely low during cooling, causing moisture condensation that easily leads to mold growth. Remember to turn off the AC compressor a few minutes before parking, letting the fan run to dry out the moisture. Don't skimp on the cabin filter either - I usually replace mine every six months, otherwise trapped pollen and dust can ferment and stink inside. If the smell is really strong, get a professional deep cleaning at an auto shop where they spray disinfectant foam through the ducts and evaporator. After treatment, it'll feel fresh like a new car again.

[DiCorey]

I encountered the issue of strange odors from the AC, and I specifically asked the technician during my last maintenance visit. The most common cause is the AC filter not being replaced for too long, clogged with dust and pollen, which eventually decomposes over time. Another reason is condensed water not draining properly and staying in the pipes, turning into a breeding ground for bacteria. This problem is especially common after the rainy season. The solution is actually simple: buying a new filter and replacing it yourself takes just five minutes. If the smell is really strong, take it to a shop and have them clean the air ducts with a specialized cleaner—it doesn’t cost much, but the effect is immediate.

[LeJoy]

I've researched the issue of AC odors, and the culprit is the microorganisms hiding in the evaporator box. During cooling, the surface temperature of the box can drop to around zero degrees Celsius, and the residual water droplets after parking become a breeding ground for mold. The sour smell we detect comes from the metabolic byproducts of these little organisms. To address this, follow three steps: First, replace the blackened filter. Then, use foam cleaner to spray and clean the air intake. Finally, start the car to let the dirty water drain out through the chassis drainage hole. In daily use, I open the windows for ventilation at traffic lights and regularly clean fallen leaves from the windshield to prevent debris from entering the AC air intake.