The cabin heating system is an important system that provides comfort for the passengers when the temperature is cool or cold. This system works in conjunction with the engine cooling system to provide the warm air that is desired. The hot coolant that is available within the engine cooling system is the source of fluid that is needed to deliver heat to the duct system. This chapter will cover the operation of these systems as well as diagnosis and repair strategies that are needed to keep the system working at a high level.
The engine cooling system is a vital part of any internal combustion engine because it works to keep the engine in a safe temperature range under all types of operating conditions. Heat is generated in the engine when the fuel is combusted to produce the energy to create power. Unfortunately, only about one-third of the heat energy contained in gasoline or diesel fuel is transmitted into power. About one-third of the heat energy is removed through the exhaust system, and about one-third of the heat energy is absorbed by the coolant that is pumped through the engine block, cylinder heads, and intake manifold.
This heated coolant is then pumped to a large heat exchanger located in the front section of the vehicle. This heat exchanger is called the radiator and it releases the heat to the surrounding air as it is forced past the core section of the radiator. The engine cooling system is designed to build up pressure as the engine heats up. This added pressure raises the boiling point of the coolant, which is desirable to prevent the system from boiling over during high-load conditions.
The engine cooling system uses liquid coolant to remove heat from the engine and carry it to the radiator. The cabin heating system uses this hot coolant to heat the cabin by forcing it through the heater core, which is located near the cowl panel or under the instrument cluster in the duct
