Where is the water valve of BMW 3 18 heater?

BMW 3 18 warm air water valve is located between the main engine water tank and the warm air water tank. The warm water valve is located between the main water tank and the engine warm water tank. The warm air water valve is the warm air switch of the automobile heater. The working principle of the automobile heater is that the radiator in the heater is connected with the circulating water of the engine through the inlet and outlet water pipes, and the water valve is a switch.