Cooling, heating and air conditioning systems

Ford Sierra / Ford Sierra Service Manual / Cooling, heating and air conditioning systems

General information and precautions

General information

The cooling system is of pressurised type, and consists of a front mounted radiator, coolant pump, cooling fan, wax type thermostat, and an expansion tank.

The radiator matrix is manufactured from honeycombed metal, and the end tanks are made of plastic. On automatic transmission models, the right-hand end tank incorporates the transmission fluid cooler.

The coolant pump is located on the front face of the engine block, and is belt-driven.

The pump is of the impeller type.

The cooling fan draws cold air over the radiator matrix to assist the cooling process when the forward speed of the vehicle is too low to provide sufficient cooling airflow, or the ambient temperature is unusually high. SOHC models have a thermo-viscous fan, whereas CVH and DOHC models have an electrically-operated fan.

The thermo-viscous fan is controlled by the temperature of the air behind the radiator.

When the air temperature reaches a predetermined level, a bi-metallic coil commences to open a valve within the unit, and silicon fluid is fed through a system of vanes. Half the vanes are driven directly by the coolant pump, and the remaining half are connected to the fan blades. The vanes are arranged so that drive is transmitted to the fan blades in relation to the viscosity of the silicon fluid, and this in turn depends on ambient temperature and engine speed. The fan is therefore only operating when required, and compared with direct-drive type fans represents a considerable improvement in fuel economy, drivebelt wear and fan noise.

The electrically-operated fan is switched on by a temperature sensor mounted in the thermostat housing when the temperature reaches a predetermined level. The fan is therefore only operating when required, and like the thermo-viscous fan, offers a considerable advantage over direct-drive type fans.

A thermostat is fitted. Its purpose is to ensure rapid engine warm-up by restricting the flow of coolant to the engine when cold and also to assist in regulating the normal operating temperature of the engine.

The expansion tank incorporates a pressure cap which effectively pressurises the cooling system as the coolant temperature rises, thereby increasing the boiling point of the coolant. The tank also has a further degas function. Any accumulation of air bubbles in the coolant is returned to the tank and released in the air space, thus maintaining the efficiency of the coolant. The pressure cap also incorporates a vacuum relief valve which prevents a vacuum forming in the system as it cools.

The system functions as follows. Cold coolant in the bottom of the radiator circulates through the bottom hose to the coolant pump where the pump impeller pushes the coolant through the passages within the cylinder block, cylinder head and inlet manifold. After cooling the cylinder bores, combustion chambers and valve seats, the coolant reaches the underside of the thermostat which is initially closed. A small proportion of the coolant passes from the thermostat housing to the expansion tank, but the main circulation is through the inlet manifold, automatic choke (where applicable), and heater matrix, finally returning to the coolant pump. When the coolant reaches a predetermined temperature, the thermostat opens and hot water passes through the top hose to the top of the radiator. As the coolant circulates through the radiator, it is cooled by the flow of air to the vehicle’s forward motion, supplemented by the action of the cooling fan where necessary. By the time it reaches the bottom of the radiator the coolant is cooled, and the cycle is repeated. Circulation of coolant continues through the expansion tank, inlet manifold, automatic choke (where applicable) and heater at all times, the heater temperature being controlled by an air flap.

An air conditioning system is available as an optional extra on certain models. In conjunction with the heater, the system enables any reasonable air temperature to be achieved inside the vehicle; it also reduces the humidity of the incoming air, aiding demisting even when cooling is not required.

The refrigeration side of the air conditioning system functions in a similar way to a domestic refrigerator. A compressor, beltdriven from the crankshaft pulley, draws refrigerant in its gaseous phase from an evaporator. The compressed refrigerant passes through a condenser where it loses heat and enters its liquid phase. After passing through the dehydrator, which acts as a reservoir and filter to extract moisture from the circuit, the refrigerant returns to the evaporator where it absorbs heat from the air passing over the evaporator fins on its way to the vehicle interior. The refrigerant becomes a gas again and the cycle is repeated.

Various subsidiary controls and sensors protect the system against excessive temperature and pressures. Additionally, engine idle speed is increased when the system is in use to compensate for the additional load imposed by the compressor.

Precautions
Air conditioning refrigerant Although the refrigerant is not itself toxic, in the presence of a naked flame (or a lighted cigarette) it forms a highly toxic gas. Liquid refrigerant spilled on the skin will cause frostbite. If refrigerant enters the eyes, rinse them with a dilute solution of boric acid and seek medical advice immediately.

In view of the above points, and of the need for specialised equipment for evacuating and recharging the system, any work which requires the disconnection of a refrigerant line must be left to a specialist.

Do not allow refrigerant lines to be exposed to temperatures above 230°F (110°C) - eg during welding or paint drying operations and do not operate the air conditioning system if it is known to be short of refrigerant, or further damage may result.

Antifreeze mixture
Antifreeze mixture is poisonous. Keep it out of reach of children and pets. Wash splashes off skin and clothing with plenty of water.

Wash splashes off vehicle paintwork to avoid discolouration.

Antifreeze/water mixture must be renewed at the specified intervals to preserve its anticorrosive properties. In climates where antifreeze protection is unnecessary, a corrosion inhibitor may be used instead - consult a Ford dealer. Never run the engine for long periods with plain water as coolant.

Only use the specified antifreeze as inferior brands may not contain the necessary corrosion inhibitors, or may break down at high temperatures. Antifreeze containing methanol is particularly to be avoided, as the methanol evaporates.

The specified mixture is 45 to 50% antifreeze and 50 to 55% clean soft water (by volume). Mix the required quantity in a clean container.

Cooling system - draining

Refer to Chapter 1, Section 46.

Cooling system - flushing

Refer to Chapter 1, Section 46.

Cooling system - filling

Refer to Chapter 1, Section 46.

Cooling, heating and air conditioning systems

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