What is the difference between internal circulation and external circulation?

[MacErin]

Internal circulation means the air only circulates inside the vehicle, while external circulation connects the interior air with outside air. Internal circulation: The air only circulates within the vehicle without exchanging with outside air. Internal circulation blocks polluted gases by closing the airflow passage between the interior and exterior. Its main function is to effectively prevent external dust and harmful gases from entering the cabin. External circulation: The interior air is connected with outside air. External air flows in through the front intake duct and exits through the rear outlet. External circulation replenishes fresh air. When driving in congested urban areas, the cabin may fill with exhaust fumes, which is caused by using external circulation.

[CaydenLynn]

I've been driving for over a decade, and the difference between recirculation and fresh air modes is quite simple. Recirculation mode reuses the air inside the car without drawing in outside air. This cools the car faster in hot weather, avoids exhaust fumes when stuck in city traffic, and saves a bit of fuel. The downside is prolonged use can make the cabin stuffy with high CO2 levels, causing dizziness—I usually switch to fresh air mode after half an hour to ventilate. Fresh air mode draws in outside air, ensuring oxygen supply and freshness, especially on highways where higher speeds allow rapid defogging—it clears foggy windshields quickly. The key is switching based on road conditions: recirculation in cities, fresh air on highways. Remember not to overuse recirculation to avoid oxygen deprivation.

[McJulian]

As a young driver, I believe the choice between recirculation and fresh air modes mainly depends on air quality and comfort. Recirculation mode locks in the cabin air, providing stronger cooling or heating effects. On scorching summer days when the car's been baking in the sun, turning it on cools things down within minutes. However, I worry prolonged use might stale the air, potentially causing fatigue or headaches, so I only use it briefly during high pollution periods. Fresh air mode introduces outside air, improving ventilation. When air quality is good, this keeps the cabin fresh and comfortable while effectively reducing humidity to prevent window fogging that could obstruct visibility. From a health perspective, I frequently use fresh air mode for breathing, especially during long-distance or highway driving, as it helps maintain mental clarity. Don't forget to check your AC system - a dirty filter can compromise its performance.

[StTeagan]

The difference between recirculation and fresh air modes lies in the air source. In recirculation mode, the AC system only processes interior air, which is ideal for rapid cooling/heating and prevents external dust/odors from entering; the drawback is stale air requiring periodic switching. Fresh air mode draws outside air to improve oxygen levels, remove humidity, and defog windows. I use it on mountain roads or in good weather to maintain freshness. Remember to combine modes according to driving conditions.