Why is there an odor when the car's external air circulation is turned on?

[Gutierrez]

The reasons for odor when the air conditioning is turned on are as follows: 1. Accumulation of dust over prolonged use: After years of use, the indoor filter and internal copper plates of the air conditioning system can accumulate a certain amount of dust. When this accumulation reaches a certain level, it can produce an odor, which is then dispersed into the air when the air conditioning is turned on. 2. Long-term moisture inside the air conditioning system promotes mold growth: After cooling or heating, the indoor unit of the air conditioning system often retains moisture. If the air conditioning is turned off immediately without a drying or anti-mold function, this moisture remains inside, leading to mold growth over time and the natural production of a musty smell.