What is the difference between the internal circulation and external circulation of car air conditioning?

[CollinDella]

Here are the specific differences between the internal circulation and external circulation of car air conditioning: 1. Symbols: The internal circulation symbol is a circular arrow inside a car graphic; the external circulation symbol is an arrow entering the car from outside. 2. Working methods: Internal circulation draws air from inside the car, creating an airflow cycle within the vehicle. Its main function is to effectively prevent external dust and harmful gases from entering the car. External circulation draws air from outside the car, directs it to the air conditioning system for heating or cooling, and then blows it out from the vents. 3. Usage: Internal circulation heats up the car faster in winter and cools it down faster when the air conditioning is on in summer. It can also be used on smoggy days. External circulation is used for defrosting in winter or defogging in summer, as the air drawn from outside is richer in oxygen and drier, making it more effective for defrosting or defogging.

[StClaire]

Let me explain in detail the difference between recirculation mode and fresh air mode, based on my over 20 years of driving experience. Recirculation mode is like closing all windows and only circulating the air inside the car; fresh air mode is like opening a small window, allowing outside air to continuously flow in. I usually use recirculation mode in traffic jams to prevent exhaust fumes from entering the cabin, especially the choking black smoke from diesel vehicles. But keeping recirculation on for more than half an hour can make people feel stuffy, so I switch to fresh air mode to ventilate. Using recirculation mode on highways can save some fuel because the AC doesn't have to cool down hot incoming air. However, it's better to use fresh air mode on rainy days to prevent windshield fogging—this trick has saved me many times. The key is to switch flexibly rather than sticking to one mode. Also, for the first three months with a new car, I recommend using fresh air mode more often to help dissipate formaldehyde odors.