Should the car's cool air use internal or external circulation?

[HarperFitz]

When using the car's air conditioning, both internal and external circulation can be used, as there are no strict requirements. The best practice is to alternate between internal and external circulation. Here are the correct steps for using the air conditioning in summer: 1. After entering the car, first open the windows for ventilation to allow the interior to cool down. Open the doors and windows to lower the temperature inside before turning on the air conditioning; 2. Start with internal circulation to achieve the fastest cooling effect; 3. Once the interior temperature has dropped to a comfortable level, switch to external circulation to maintain fresh air inside the car. Note that in summer, the temperature inside the car is often higher than outside, so using internal circulation alone may slow down the cooling process.