Cooling, heating and air conditioning systems
Engine cooling system
All vehicles covered by this manual employ a pressurized engine cooling system with thermostatically controlled coolant circulation. An impeller-type water pump mounted on the front of the engine pumps coolant through the engine. The coolant flows around each cylinder and toward the rear of the engine. Cast-in coolant passages direct coolant around the intake and exhaust ports, near the spark plug areas and in close proximity to the exhaust valve guides. Because of the design of the accessories, pulleys and drivebelts, some engines are equipped with reverse rotating water pumps, cooling fans and viscous fan clutches. Always check with a parts department and install only components marked REVERSE.
A wax-pellet type thermostat is located in a housing near the front of the engine. During warm up, the closed thermostat prevents coolant from circulating through the radiator. As the engine nears normal operating temperature, the thermostat opens and allows hot coolant to travel through the radiator, where it’s cooled before returning to the engine.
The radiator is sealed by a pressure cap. This raises the boiling point of the coolant and this higher boiling point increases the efficiency of the radiator. If the system pressure exceeds the cap’s pressure relief value, then the excess pressure in the system forces the spring-loaded valve in the cap off its seat and allows the coolant to escape through the overflow tube and into the coolant reservoir. When the system cools, the coolant is drawn from the reservoir back into the radiator. This type of system is known as a closed design because coolant that escapes past the pressure cap is saved and reused.
The radiator cooling fan is mounted on the front of the water pump on gasoline engines or the fan pulley on diesel engines. Gasoline models are equipped with a viscous fan clutch while diesel models are equipped with an electronic viscous clutch that is controlled by the Powertrain Control Module (PCM).
Heating system
The heating system consists of a blower fan and heater core located in the heater/air conditioning unit under the dash, the hoses connecting the heater core to the engine cooling system and the heater/air conditioning control head on the instrument panel. Hot engine coolant is circulated through the heater core. When the heater mode is activated, a flap door opens to expose the heater box to the passenger compartment. A fan switch on the control head activates the blower motor, which forces air through the core, heating the air.
Air conditioning system
The air conditioning system consists of a condenser mounted either in front of (diesel models) or adjacent to the radiator (all other models), an evaporator mounted adjacent to the heater core under the dash, a compressor mounted on the engine, an accumulator mounted near the firewall and the plumbing that connects all of these components.
A blower fan forces the warmer air of the passenger compartment through the evaporator core (sort of a radiator-in-reverse), transferring the heat from the air to the refrigerant. The liquid refrigerant boils off into low-pressure vapor, taking the heat with it when it leaves the evaporator.