Control Valves (Heating)

To heat vehicle cabins, most vehicles use the coolant of the engine as a source of heat. The coolant flows through a small heat exchanger called the “heater core”. A fan circulates air through this core when we need heat to warm up the cabin. The heater control valve controls the amount of coolant that flows through the heater core.

The heater core does not require energy to operate and manages to recycle the residual heat if correctly used. It operates like a small radiator.
From the fan, the flow of air is controlled by a series of doors inside the fan box. The control valve permits precise temperature control and a dual area temperature with multiple doors.  When heat is required, the air flows through the heat core. Once the cabin is hot, the airflow is diverted around the core. 

Most modern systems first cool and dehumidify the air and then heat it to the desired temperature. These valves can be controlled mechanically, by vacuum or electronically.