What Causes the Unpleasant Odor When Turning on the Car Air Conditioner?
3 Answers
When the car air conditioner is turned on, an unpleasant odor may occur because the temperature of the evaporator can drop to nearly 0°C during operation, similar to a refrigerator, which inhibits fungal growth. However, once the compressor stops working and the refrigerant ceases to circulate, the temperature of the evaporator rises, creating a warm and humid environment on its surface—ideal conditions for fungal growth. To eliminate the odor, simply manually turn off the air conditioning cooling (usually the AC button) a few minutes before shutting off the engine, but keep the blower running for a while (i.e., leave the fan on for 1 to 2 minutes). This allows the evaporator to return to ambient temperature and quickly evaporate any moisture on its surface, preventing the damp conditions that foster fungal growth and thus eliminating the odor.
When the car's air conditioning emits an unpleasant odor, I believe the most common cause is the growth of mold or bacteria on the evaporator. When the AC is on, the low temperature inside the car causes moisture to condense on the evaporator. If the fan doesn't dry it out after parking, this moisture becomes a breeding ground for mold, resulting in a musty or earthy smell. To prevent this, I make it a habit to turn off the AC a few minutes before parking but keep the fan running to dry out the system. DIY cleaning is simple—just use an AC cleaning spray on the air intake, and it’ll be done in minutes. Alternatively, regularly replacing the cabin air filter (even an inexpensive one can last over six months) helps. Environmental factors also play a role; for instance, rainy or high-humidity conditions accelerate mold growth, so parking in well-ventilated areas is advisable. This issue isn’t just annoying—it affects in-cabin air quality. Addressing it early prevents more costly repairs later.
When I first turn on the AC and notice an unpleasant odor, it's usually due to bacterial growth in the AC system. After the evaporator and ducts become damp, bacteria can easily multiply, producing a sour or musty smell. I've learned to turn off the AC a few minutes before parking to let the fan blow out excess moisture. DIY solutions are quite simple: use a spray cleaner for treatment, or on a sunny day, park the car and run the heater for half an hour to dry it out. Don't forget to replace the cabin air filter—a dirty one can block airflow. Additionally, if the odor comes from outside, like pollen or pollution entering the intake, try switching to recirculation mode to block it. Regularly doing these small tasks can significantly reduce odors, making maintenance easy even for beginners.
