Function of the heater control valve

The heater control valve is used as a shut off valve to control coolant flow through the heater core. There are many types and designs of heater control valves. The gas heater control valve can be operated by vacuum or cable controls. Vacuum can be used to open the valve or it can be used to close the valve. Cable controlled gas heater valve normally operate in conjunction with the cable that controls the vehicles interior temperature level.