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

[McAnna]

Internal air circulation means that the air only circulates inside the car, driven by the blower to cycle the cabin air. External air circulation, on the other hand, connects the interior of the car with the outside. While driving, airflow automatically enters the cabin due to wind pressure, and when stationary, outside air can still enter the blower through the air ducts and be blown into the cabin. Below is an introduction on when to use each mode: 1. External air circulation: For a newly purchased car, it is essential to keep the external air circulation mode on as much as possible to maintain airflow between the inside and outside of the car. This helps to quickly release harmful gases from the cabin. Additionally, during long highway drives, keeping the internal air circulation mode on for too long can lead to insufficient oxygen levels in the cabin, causing driver fatigue and potentially leading to accidents. In such cases, switching to external air circulation can replenish fresh air inside the car. 2. Internal air circulation: During regular driving, we mostly use the internal air circulation mode. However, it is crucial to switch to internal air circulation during heavy traffic, as the density of exhaust fumes in the air increases with congestion. This mode effectively prevents outside exhaust from entering the cabin, protecting occupants from harm. It is also advisable to use internal air circulation during sandstorms or dusty weather, as it not only prevents dust from entering the cabin but also reduces the impact of sand on the air conditioning filter.

[RyanLee]

When I first started learning to drive, I was curious about the difference between these two buttons. The recirculation mode essentially closes the windows to prevent outside air from entering, only circulating the hot or cold air inside the car. It's suitable for situations like when you first get in the car and it's extremely hot—turning on the AC cools it down quickly—or when stuck in traffic to avoid inhaling exhaust fumes. However, it shouldn't be used for too long, as the air can become stuffy and make you drowsy. The fresh air mode draws in fresh air from outside, which is great for ensuring sufficient oxygen and smooth breathing during highway driving or when there are many passengers. It also helps prevent window fogging on rainy days. I need to figure out the right timing—for example, using recirculation more during smoggy days for self-protection, and switching to fresh air on sunny days for comfort. Operationally, it's just a matter of pressing the button to switch modes, which is quite convenient, so don't worry about complexity. Driving safety comes first.

[VonOscar]

I've been driving for over 20 years and frequently switch between recirculation and fresh air modes to solve practical problems. The recirculation mode tightly closes the windows, allowing the AC to only circulate cabin air. The advantage is faster temperature adjustment with higher efficiency, like cooling down a steamer, but the downside is poor air circulation causing dizziness with prolonged use. The fresh air mode introduces outside air through a small gap, keeping you refreshed during long drives by preventing CO₂ buildup or fogging that affects visibility. I recommend using fresh air mode on highways for better breathing, while switching to recirculation in polluted urban areas. On rainy days, I activate fresh air mode with the defog button to prevent blurred vision – this simple button combination makes journeys safer and more comfortable, so don't overlook it.

[AniyahDella]

At my age, health is a priority, so choosing the right car air conditioning mode is essential. The recirculation mode locks in the internal air and prevents outside air from entering, which is ideal for protecting your respiratory system in poor external conditions like heavy dust or fog. However, prolonged use can lead to oxygen deprivation and stuffiness, so moderation is key. The fresh air mode draws in external fresh air to promote ventilation. Using this mode during long drives helps refresh the mind, prevent fatigue, and is particularly beneficial for health. On rainy days, combining fresh air mode with windshield defogging ensures safety and prevents accidents. I prefer manually selecting the mode based on weather conditions to make driving more comfortable and relaxed.