What is the difference between internal and external air circulation in a car?

[VivianMarie]

The difference between internal and external air circulation in a car: Internal circulation means the air inside the car is heated or cooled and then recirculated within the car; external circulation means air from outside the car is heated or cooled and then brought into the car, allowing gas exchange between the inside and outside of the car. Specific details are as follows: 1. Internal circulation keeps the air inside the car circulating in a closed loop, represented by an icon of a closed car interior with a circular arrow; external circulation brings outside air into the car, represented by an icon of an open car with an external air arrow pointing into the car. 2. Whether using the heater or air conditioner, start with internal circulation. Although the temperature inside the car will drop, the carbon dioxide exhaled by passengers will increase. Therefore, it's best to switch to external circulation every hour to refresh the air. 3. When turning on the air conditioner for cooling or heating, first activate internal circulation to quickly lower or raise the temperature inside the car. Once the temperature stabilizes, switch to external circulation to exchange air with the outside. 4. If the outside air quality is poor, such as in heavy traffic with high exhaust emissions or in a poorly ventilated underground garage, avoid using external circulation. When driving on the highway, do not open the windows; simply use external circulation.

[AnastasiaLee]

The most fundamental difference between recirculation and fresh air modes lies in the air source. Recirculation recycles the existing air inside the car, equivalent to breathing with windows closed; while fresh air mode introduces outside air, like opening windows for ventilation. I flexibly switch between them during my daily commute: using recirculation for rapid cooling when first entering the car in summer, then switching to fresh air mode for ventilation after temperature drops; activating recirculation in traffic jams to block exhaust fumes and dust; employing fresh air mode during highway trips to maintain airflow and prevent drowsiness. Fresh air mode works better against window fogging on rainy days as it reduces temperature differences. Remember to regularly replace the cabin air filter - otherwise, fresh air mode may introduce dust and affect health.

[GarrettLynn]

I'm quite concerned about the air quality inside the car, and the usage differences between these two modes are significant. The recirculation mode is like breathing the same air in a confined space. Prolonged use can increase carbon dioxide concentration, making people drowsy, so I basically switch to the fresh air mode for a few minutes every half hour to ventilate. The fresh air mode brings in outside air, but it needs to be turned off during smoggy days. On the highway, keeping the fresh air mode on is most comfortable, as the wind blowing into the car is particularly refreshing. When using the air conditioner, it's also important to note: using recirculation mode cools faster and saves more fuel, but the windows are prone to fogging up; using fresh air mode cools slower but is less likely to cause fogging. It's wisest to switch flexibly based on road conditions and weather while driving.

[DelAustin]

When I first started driving, I didn't understand these two buttons either. Once on a long trip, I kept using the recirculation mode with warm air and ended up feeling extremely dizzy. Later I learned: the arrow circling inside the car means recirculation mode, which keeps recirculating the same cabin air; the arrow coming from outside into the car means fresh air mode, which brings in outside air. In summer, turning on recirculation before AC cools the car much faster; in winter, using fresh air mode helps defog windows quickly. Remember to use fresh air mode on highways - prolonged recirculation can cause drowsiness. Just remember to switch between modes regularly and you'll be fine.

[Kaylee]

After driving for over a decade, I've found that using recirculation mode significantly saves fuel. When cooling, recirculation cools the cabin faster because the AC only processes the existing air inside the car; whereas fresh air mode continuously cools incoming hot air, putting more load on the compressor and consuming more fuel. My habit is to start with recirculation for rapid cooling, then switch to fresh air mode for ventilation once comfortable. However, prolonged recirculation can cause window fogging - switching to fresh air clears fog faster. Interestingly, fresh air mode is more efficient at highway speeds because high-speed external airflow reduces AC workload. Smart toggling between modes balances eco-friendliness and comfort.

[ChristianDella]

I used to always use the recirculation mode with the heater on during winter drives, but after two continuous hours, I'd feel dizzy and blurry-eyed. Later, I learned that insufficient oxygen in a confined space can cause fatigue. Now, I'm very mindful of the duration I use recirculation—I switch to fresh air mode for ventilation after no more than an hour. On smoggy days, recirculation is a must to keep PM2.5 out; on highways, fresh air mode helps stay alert and safe. The sequence for summer cooling is crucial: first recirculation to cool down, then switch to fresh air to maintain. Regularly changing the cabin air filter is important—once, I noticed a strange smell when using fresh air mode, and replacing the filter fixed it.