What Causes the Bad Smell in Car Air Conditioning?
3 Answers
Car Air Conditioning Smell Causes: The unpleasant odor that often occurs when turning on the car air conditioning is mostly due to mold growth in the evaporator box and ventilation ducts. Air entering the car passes through the evaporator box to be cooled or heated before being blown out through the vents as warm or cool air. During this process, bacteria, dust, and even insect remains can accumulate in the evaporator box and ventilation ducts. Over time, this buildup leads to bad smells when the air conditioning is used. Solutions: 1. The best method is to choose an open, sunny area, open the car doors, turn on the natural air setting, set the external circulation to maximum (without turning on the air conditioning), or even better, use the heater setting. Let it run for 5-6 minutes to blow out the dust. 2. The air conditioning filter should generally be replaced once a year. However, if there are frequent sandstorms or other harsh weather conditions, replacing it every few months may be necessary. If the filter is only superficially dirty, it can be simply blown clean. However, if it is heavily soiled, cleaning is not recommended as it can enlarge the filter pores, significantly reducing its filtering effectiveness.
My neighbor Brother Zhang, who has worked at a 4S dealership for eight years, says that nine times out of ten, a foul smell from the AC is due to mold in the evaporator. During summer, when the AC is cooling, condensation forms on the evaporator's surface. After turning off the engine, the moisture trapped in the pipes can breed mold—just like the musty smell of a wet towel left unwashed. Also, if the cabin air filter hasn't been replaced for too long, it accumulates dust and dead insects, causing the air to smell earthy. Some owners have even had leaves fall into the AC intake, rotting and causing a stench. It’s crucial to turn off the AC three minutes before parking and just run the blower to dry out the pipes, preventing mold growth. Remember to replace the filter every season, and if the smell is severe, use a specialized foam cleaner for a thorough disinfection—never mask it with perfume, as that only makes it worse.
Last time when I drove the company's GL8 to pick up clients, the AC blew out a foot odor smell, which was extremely embarrassing. The mechanic told me it was mainly due to issues with the evaporator and the air filter. In summer, when the AC is on, the evaporator condenses moisture like a fridge, and after turning off the engine, water droplets accumulate on the aluminum sheets, turning them into a breeding ground for mold. If the air filter isn't changed for half a year, it becomes clogged like a dust filter, blowing out stale, earthy smells when the air is on. Upon inspection, they even found a dead cockroach stuck in the blower. Now, I always turn off the AC five minutes early to let the fan dry out the ducts, and I make sure to change the filter with every season change. If you notice any odd smells, address them immediately—inhaling too much bacteria can easily lead to respiratory infections, especially for families with kids, who should be extra cautious.
