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

[DelValeria]

The differences between the internal circulation and external circulation of car air conditioning are: 1. Different icons: The internal circulation icon is a closed car with a circulating arrow inside; the external circulation icon is an unclosed car with an air arrow pointing into the car from the outside. 2. Different working methods: Internal circulation allows the air inside the car to circulate when the car is closed; external circulation brings air from outside the car into the interior. 3. Different functions: The function of internal circulation is to heat or cool the air inside the car before sending it back into the car; the function of external circulation is to heat or cool the air from outside the car before sending it into the car, meaning gas exchange between the inside and outside of the car.

[ORobert]

I've been driving a taxi for over ten years, let me explain these two AC modes. The fresh air mode draws in outside air, like opening a window but without wind noise. Recirculation mode just keeps recycling the air inside the cabin. Always switch to recirculation in traffic jams - otherwise you'll get all the exhaust fumes from the vehicle in front, that diesel smell can choke you to death. When first getting in a hot car in summer (feels like a steamer inside), I first use fresh air mode to vent the hot air, then switch to recirculation for faster cooling. On long trips, it's best to switch between modes every half hour - staying on recirculation too long makes the air stale and can cause drowsiness. On rainy days when the windshield fogs up, just turn on fresh air mode for 2-3 minutes and the fog clears right up - super practical trick.

[AvaLee]

Having a child with allergies at home, I pay extra attention to the air quality inside the car. The main difference between external and internal air circulation is the source of air: external circulation is like opening a window for ventilation, while internal circulation is like changing air with doors and windows closed. When my child is in the car, I mostly use external circulation to bring in fresh air and dilute formaldehyde and odors inside the car. However, on smoggy days or when passing through tunnels, I immediately switch to internal circulation and wait for the air purifier to filter out the particles before switching back. For new cars, I recommend using external circulation more often to dissipate odors, but remember that using internal circulation makes the air conditioning more efficient and saves fuel, while also heating up faster in winter.

[AlanaLee]

My SUV has been running for five years, and I've found that smartly switching between these two modes can save a lot on fuel costs. The recirculation mode reuses the existing air inside the car, preventing the loss of cool air when the AC is on in summer, which saves about 10% more fuel compared to the fresh air mode. Once the temperature drops, you can switch to fresh air mode for ventilation. However, never use recirculation mode the entire time, as the carbon dioxide level inside the car will exceed safe limits after half an hour, causing dizziness. The most practical use is during sandstorms or when passing by a garbage dump—switching to recirculation mode blocks out the stench and dust. Remember to replace the cabin air filter every six months; otherwise, using fresh air mode might blow the accumulated dust from the filter back into the car.

[AlexisAnn]

Moms who shuttle their kids to and from school know all too well the smell of barbecue smoke from street vendors when the air recirculation is off, not to mention the occasional whiff of car exhaust. I usually keep the air recirculation on in the city and only switch to fresh air mode in the suburbs. I used to worry most about my kid getting carsick, but then a doctor pointed out that recirculated air can actually make motion sickness worse. Now, I make it a habit to roll down the windows for five minutes to air out the car before starting the engine, then drive with the fresh air mode on. When it rains and the windshield fogs up, turning on the fresh air mode along with the defogger works like a charm—clear visibility in just two minutes. Just remember not to point the air vents directly at the kids to avoid catching a cold.

[GemmaMarie]

Experienced drivers who frequently drive on highways know that the air recirculation mode should be switched according to road conditions. I always switch to recirculation mode before entering a tunnel and switch back 500 meters after exiting to avoid the turbid air. When using fresh air mode, the wind speed feels gentler and less harsh, making it suitable for ventilation during long-distance driving. In summer, when resting at service areas, opening windows may invite mosquitoes, so I use the fresh air mode at a low speed for ventilation. The most practical tip is defogging in winter: pressing the front windshield defogging button automatically switches the system to fresh air mode, utilizing the dry outside air for quick defogging. If there's an unpleasant odor from the air conditioning, it's likely time to replace the filter.