What is the button for the heater in a sedan?

[StFrancisco]

The heater in a sedan is controlled by the temperature adjustment button. The method to turn on the heater is as follows: 1. Start the engine and allow it to warm up until the engine temperature gauge needle reaches the middle position; 2. Turn on the heating function of the air conditioning system while setting the air circulation to external circulation to expel the cold air from the vehicle cabin; 3. After 2 to 3 minutes, switch the air circulation to internal circulation. The air conditioning system installed in sedans serves the following purposes: 1. It can cool, heat, ventilate, and purify the air inside the cabin; 2. It provides a comfortable environment for passengers; 3. It reduces driver fatigue and enhances driving safety. The components of a sedan's air conditioning system include: compressor, electronically controlled clutch, condenser, evaporator, expansion valve, receiver-drier, pipelines, condenser fan, vacuum solenoid valve, and idle speed controller.