Why does the Audi A3's internal air circulation automatically turn off?

[OClayton]

Automatic air conditioning can adjust between internal and external circulation based on the set temperature. Here are the relevant explanations: 1. External circulation: This mode draws air from outside the vehicle, directs it through the air conditioning system for heating or cooling, and then blows it out through the vents. External circulation replenishes fresh air and improves cabin air quality. However, in extremely hot and dry weather, using external circulation requires the AC compressor to work continuously to cool the outside hot air, which consumes additional fuel. 2. Internal circulation: This mode recirculates the air inside the vehicle cabin. The AC system draws in cabin air, cools it, and then returns it to the cabin. When the cabin temperature reaches the set value, the AC compressor stops working, reducing engine load. Therefore, the faster the cabin temperature reaches the set value, the sooner the engine load decreases, resulting in lower fuel consumption.