When the car's heater is turned on, the coolant, which is heated by the engine, flows through the heater matrix. As the air from the car's blower motor passes through the heater matrix, it gets heated by the matrix's warm surface and is then distributed throughout the car's interior via the vents.
By controlling the flow of coolant through the heater matrix and the speed of the blower motor, the driver can regulate the temperature of the air that is blown into the car. This allows the occupants of the car to maintain a comfortable temperature inside the vehicle, regardless of the external temperature.
Additionally, some heater matrices are designed to also function as part of the car's air conditioning system during warm weather. In such cases, cold refrigerant instead of hot coolant flows through the heater matrix, helping to cool the incoming air.
