Why does the car air conditioner emit a sour smell after turning off the AC?
2 Answers
Reasons for the sour smell after turning off the AC in a car air conditioner: When mold and fungi encounter a suitable environment, they rapidly multiply, and during this process, they emit a sour and foul odor. Here are the specific reasons: Humid environment: When the car air conditioner is operating, the evaporator coil is in a cold environment and encounters relatively hot external air, leading to condensation. Consequently, the humid conditions in the evaporator coil and ventilation ducts, along with the dust accumulated on their surfaces, create an ideal breeding ground for mold and fungi. Odor emission: Once mold and fungi find a suitable environment, they quickly multiply into colonies. During this reproduction process, they produce a putrid odor characteristic of decaying matter.
Recently, my own car encountered the same issue—a sour smell after turning off the AC. After some research, I found out it's caused by mold buildup in the evaporator. When the AC is running, condensation water accumulates, especially if the compressor is turned off before the moisture fully evaporates, allowing bacteria to thrive. Over time, when the fan blows air, it carries this musty odor, which smells sour. The solution is actually quite simple: I recommend getting a professional cleaning of the evaporator and air ducts, or using an AC disinfectant spray yourself. Prevention is key—for example, turning off the AC a few minutes before parking and running the fan at high speed for about 10 minutes to dry out any remaining moisture. Also, replace the cabin air filter regularly, as dust buildup can encourage mold growth. I’ve made it a habit to service the system quarterly, and now the car feels much fresher.
