Why does the car smell bad when the air conditioner is first turned on?

[MacEzra]

The reasons why the car smells bad when the air conditioner is first turned on are: 1. The air conditioner evaporator is moldy, and bacteria gather and multiply on it; 2. The air filter has not been replaced for a long time. The solutions to the bad smell when the car air conditioner is first turned on are: 1. Replace the air filter; 2. Run the fan at high speed; 3. Clean the air conditioner ducts. Precautions for using the car air conditioner include: 1. Turn off the AC switch when starting or accelerating sharply; 2. Do not set the air conditioner temperature too low; 3. Control the direction of the air outlet; 4. Do not turn on the air conditioner immediately after the car has been exposed to the sun; 5. Turn off the air conditioner before turning off the engine when parking.

[Frieda]

I've also experienced the foul smell when turning on the car AC. It's most likely due to mold growth in the evaporator or AC ducts, caused by residual moisture that didn't dry completely after using the cooling function. Additionally, if the cabin air filter is too dirty, the accumulated dust and bacteria can be blown out by the fan, creating unpleasant odors. I usually turn off the AC a few minutes before parking and let the fan run to dry the evaporator. Also, remember to replace the filter regularly, ideally every six months or annually. If the smell is unbearable, you can try using a specialized AC cleaning spray—just remove the filter and spray it into the air intake; it's quite simple to do yourself. If that doesn't work, a professional deep cleaning at a shop might be necessary, where they disassemble and clean the evaporator box thoroughly.

[LeJohnny]

Every time I turn on the AC, there's a sour smell? This is mostly because the air conditioning system is too damp inside. After cooling and parking, water droplets remain on the evaporator, and combined with the enclosed environment, fungi and bacteria multiply, causing the odor. Especially in older cars, accumulated dust and mold clusters in the air ducts get blown out, making the smell particularly strong. I recommend first replacing the AC filter. If that doesn’t help, try a disinfectant spray. Turning off the AC five minutes before parking and just running the fan to let hot air dry out the ducts is especially effective. Also, avoid smoking in the car—the mix of smoke and mildew smells is even worse. Regular AC maintenance is crucial too. I’ve had steam disinfection done at a car wash, and the whole process significantly reduced the odor.

[LylaMarie]

When the car air conditioner emits a foul odor upon startup, it's usually due to issues with the evaporator or air ducts. The evaporator forms condensation during cooling, and if water isn't properly drained after parking, it can lead to mold and bacterial growth. Accumulated dust in the air ducts can also cause unpleasant odors when blown out. I've dealt with similar cases before—first check if the cabin air filter needs replacement. Then try self-cleaning methods: blast the heater at maximum setting for 10 minutes to kill some mold, or use disinfectant spray through the fresh air intake. If these don't solve the problem permanently, you'll need a technician to dismantle the dashboard and clean the evaporator. As preventive maintenance, avoid turning off the AC immediately after parking; allow some time to dry out residual moisture, which helps prevent strange odors.