The clean side of the air filter is facing upwards. Here is how to distinguish the air filter:
1. The arrow direction of the car air-conditioning filter element actually indicates the front and back of the air-conditioning filter element. The direction of the arrow indicates the airflow direction, that is, the installation direction. The arrow points upwards to the front, and it needs to be installed facing the airflow direction;
2. The front and back can also be judged by observing the surface of the air filter element. The ordinary wool surface is the front side, facing upwards and facing the airflow direction, and the side with the support line structure is the reverse side, back facing the airflow direction;
3. The black surface with activated carbon faces the airflow direction is the front side, and the white side faces the airflow direction is the reverse side.

The role of air filter:
1. The engine must suck in a large amount of air during the working process. If the air is not filtered, the dust suspended in the air is sucked into the cylinder, which will accelerate the wear of the piston assembly and the cylinder. Larger particles entering between the piston and the cylinder will cause serious "cylinder pull" phenomenon, which is especially serious in a dry and sandy working environment;
2. The air filter is installed in front of the carburetor or intake pipe to filter out dust and sand particles in the air and ensure sufficient and clean air to enter the cylinder;
3. Among the tens of thousands of parts and components of a car, the air filter is an extremely inconspicuous component. It is not directly related to the technical performance of the car, but in the actual use of the car, the air filter has a great influence on the service life of the car, especially the engine.