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

[LeCody]

The difference between internal and external air circulation is that internal circulation blocks polluted air, while external circulation replenishes fresh air. Here are some details about internal and external air circulation: 1. External circulation: External circulation is a process where air is exchanged between the inside and outside of the car. It draws air from outside into the air conditioning system to cool it, filling the entire car with cool air. The main benefit of external circulation is that it provides fresh air while cooling the interior. Additionally, when the outside air is dry or cold, external circulation can help defrost or defog the windows. 2. Internal circulation: During summer or winter, if you want to quickly cool or heat the car, turning on internal circulation is effective because the air does not flow in or out, allowing it to cool or heat up rapidly. In heavy traffic, it is also advisable to use internal circulation to prevent exhaust fumes from entering the car.

[BriannaLee]

As an ordinary driver with over a decade of experience, I find the difference between air recirculation and fresh air mode quite straightforward: Recirculation cycles the existing cabin air repeatedly, ideal for quick cooling when first entering the vehicle or avoiding external smoke/odors, but prolonged use degrades air quality and causes drowsiness. Fresh air mode draws outside air to maintain oxygen flow, preventing window fogging and bacterial buildup—especially useful on highways or long drives. My routine is to start with a few minutes of recirculation for rapid cooling on scorching days, then switch to fresh air to avoid dizziness from stale air. Note: Some vehicles lack auto mode, requiring manual button selection. For instance, I immediately activate recirculation in dusty construction zones to protect my respiratory system—this habit boosts efficiency and reduces AC load.

[AxelAnn]

As a new driver just starting out, I found the air recirculation and fresh air modes quite crucial when learning to use the AC: one circulates air inside while the other draws fresh air from outside. The benefit of recirculation is faster cooling - it gets chilly quickly in summer, especially blocking exhaust fumes in traffic jams. But the downside is you can't keep it on too long, or CO2 builds up and makes the cabin stuffy. Fresh air mode is the opposite - constantly bringing in outside air prevents fogging but cools slower. Last time I forgot to switch back to fresh air mode during an hour-long drive and nearly passed out from the stuffiness! So now I set a rule: must switch from recirculation after 30 minutes of driving. A reminder for fellow newbies: don't confuse the buttons - the fresh air symbol usually has an arrow pointing inward.

[FelixDella]

I prioritize a healthy lifestyle, and from an air pollution perspective, here's how I view the air circulation modes in cars: Recirculation mode recycles the already filtered air inside the vehicle, effectively blocking PM2.5 or toxic fumes. It's energy-efficient and safe for short-term use. Fresh air mode introduces external oxygen, reducing bacterial accumulation risks. However, prolonged recirculation can increase VOC concentrations affecting breathing, while fresh air mode faces external pollutant threats. My practice is to use recirculation for rapid air purification in polluted areas, and switch to fresh air mode for 20-minute ventilation on clear days to renew cabin air, ensuring optimal comfort and respiratory balance.