Climate system — general information (Audi A4 B7)

Note: The description of the climate control system is given using the example of models with a refrigeration unit.

Description of systems

The description of the climate control system is given in Chapter "Controls and operating techniques". One of the main elements of the climate control system is its block, which contains the main components: fan, radiator, evaporator and air flow distribution flaps with activators (see illustrations 7.1a-c). Before entering the air conditioning unit, outside air passes through a cabin filter designed to clean it of small particles (dust, soot, pollen, etc.); the filter should be replaced periodically (see Chapter 1). The fan is designed for ventilation of the passenger compartment, i.e. to increase the intensity of air supply to the passenger compartment of the car; the fan speed can be adjusted. To heat the passenger compartment, the coolant heated in the engine is passed through the radiator of the climate control system, giving off heat to the air passing through it. To cool the passenger compartment, a refrigeration unit is used, in which the refrigerant R134a circulating takes heat from the air supplied to the passenger compartment when the air passes through the evaporator. Along with cooling, the air is dried when passing through the evaporator, so it is recommended to turn on the refrigeration unit to reduce the humidity in the passenger compartment (for example, to speed up the removal of condensation from glass). The flaps are used to: switch between supply ventilation/air circulation modes, regulate temperature, and distribute air flows in the cabin (to the feet, to the face, on the glass and in the intermediate zones). Additional adjustment of air flows in the cabin is carried out by means of adjustable deflectors on the instrument panel. The location of the air ducts and air flow direction diagrams are shown in Illustrations 7.2a-c.





















The location of the climate control system components in the engine compartment and luggage compartment is shown in Figure 7.3.





The climate control system is controlled by an electronic control unit (see chapter "Controls and operating techniques"). The dampers are driven by electronically controlled actuators (see illustrations 7.1a-c). On models with a climate control system with a cooling function, the following sensors are additionally used:

• solar radiation sensor - measures the strength of solar radiation and transmits the obtained values to the electronic control unit of the climate control system, which, when operating in automatic mode, regulates the fan speed and the position of the flaps if necessary;
• air quality sensor - determines the composition of the air at the inlet for automatic switching between supply ventilation and circulation mode;
• heater temperature sensor, cabin air temperature sensor. The electronic control unit of the climate control system uses data from these sensors as additional ones to maintain the set air temperature in the cabin. For the correct operation of the climate control system in automatic mode, do not cover the sensors.

Description of the refrigeration unit

A schematic description of the refrigerant flows is shown in Figure 7.4.





The compressor (2), driven by a belt from the engine crankshaft, sucks in gaseous refrigerant from the evaporator (13) and compresses it. In doing so, the temperature of the refrigerant rises to 70°C.

Note: On 8-cylinder engines, a drive shaft is used instead of a belt to drive the compressor.

To ensure that the compressor sucks in only gaseous refrigerant, an accumulator (16) is installed between the compressor and the evaporator, which absorbs the mixture of steam and gas coming from the evaporator. The steam turns into gaseous refrigerant. Compressor oil that gets into the circuit does not remain in the accumulator - a special hole is provided for it. Moisture that penetrates the refrigerant circuit during assembly is captured by the filter (dehumidifier), which is located in the accumulator. Thus, the compressor sucks in gaseous refrigerant with oil from the accumulator.

Under high pressure from the compressor, the refrigerant is directed to the condenser (8), where the heat from the refrigerant is taken away by the air passing through the condenser fins. Due to this heat loss, the refrigerant changes to liquid form and is directed from the condenser to the expansion tube.

The expansion tube (12) creates a narrow section in the circuit. This narrow section reduces the flow of liquid refrigerant and divides the refrigeration circuit into low-temperature zones (not less than 1 bar) and high (no more than 20 bar) pressure. In front of the expansion tube, the refrigerant under high pressure is warm (up to 60÷70°C), and behind the tube, the refrigerant under low pressure is cold (not lower than -4°C). In front of this narrow section, there is a filter for catching dirt, and behind the narrow section, there is a mesh for spraying the refrigerant before it gets into the evaporator.



In the evaporator (13), the liquid refrigerant, cooling, returns to a gaseous state, while the air passing through the evaporator is cooled and dried. The gaseous flow of refrigerant, leaving the evaporator under low pressure, again enters the compressor through the accumulator-dryer.

Compressor oil is used to lubricate the components of the refrigeration unit and circulates in the system together with the refrigerant.

Constant condensation of moisture on the evaporator after some time of operation of the refrigeration unit creates an environment favorable for the development of bacteria and other microorganisms. Together with contaminants penetrating with outside air, they can lead to the evaporator being overgrown with microorganisms and, as a result, the appearance of a musty smell. To prevent this situation, the cabin filter should be replaced regularly - this will reduce the ingress of dirt. Ultrasound or special solutions are used to clean the evaporator, for the application of which folding sprayers are used, inserted into the air conditioning unit.

To prevent evaporator icing, the refrigeration unit automatically switches off if the outside air temperature drops to +2...+7°C, as well as if the refrigerant pressure is excessively high. If the refrigerant pressure is too low (this may indicate that there is insufficient quantity or that its circuit is depressurized) the refrigeration unit also switches off automatically.

Safety precautions when servicing a refrigeration unit

Do not open the refrigerant circuit, as refrigerant may cause frostbite if it comes into contact with your skin.

Work on the refrigeration unit must be carried out in a suitably equipped specialized workshop. Maintenance of the refrigeration unit of the system should be entrusted exclusively to trained technical personnel, trained in safe working practices using the appropriate equipment and observing the rules for depressurization, as well as familiar with the methods of collecting and storing automotive refrigerant.

Avoid contact of refrigerant with skin.

Wear safety glasses when working near a refrigeration unit; when working with refrigeration oil, additionally wear oil-resistant gloves

If refrigerant gets on your skin or in your eyes, do not rub the affected area. Immediately rinse the affected area with cold water for at least 15 minutes and seek qualified medical help. Self-medication is not allowed.

The refrigerant is stored in cylinders under pressure. Store the cylinder at a temperature not exceeding +50°C. Take measures to prevent the cylinder from falling from a height or other situations that may result in its damage.

Work should be carried out in a well-ventilated area. The refrigerant evaporates quickly, reducing oxygen availability and making breathing difficult.

The gaseous refrigerant is heavier than air and should collect relatively quickly at a low level, such as under a car.

When the refrigerant burns, a toxic gas is formed. Keep the refrigerant away from open sources of fire. Do not smoke when working with the refrigeration unit.

When welding near the refrigeration unit, do not expose it to high temperatures or open flames. Overheating may cause pressure in the refrigerant circuit to increase and cause a fire.

Cleaning the condenser or evaporator with water vapor is not permitted. Only cold water or compressed air should be used.

Refrigeration unit maintenance

Caution: Servicing the refrigeration unit requires appropriate equipment and qualifications. Follow the safety precautions listed in the subsection above.

Note: The refrigerant and refrigerant are extremely hygroscopic, so close the container and the refrigeration circuit immediately after adding them. If the refrigerant circuit has been completely emptied due to depressurization (accidents or repairs), then the desiccant should be replaced because too much moisture may have entered the system.

To improve the separation of the coolant from the refrigeration oil, let the engine run for a few minutes at low speeds (800÷1200 rpm) with the refrigeration unit running. This helps to ensure that the oil is less carried along with the coolant during pumping.

Autonomous fuel heater

An additional heater is installed on diesel models and serves to preheat the engine and interior (see chapter "Controls and operating techniques").

The location of the main components of the autonomous heater, its design and connection diagram are shown in illustrations 7.5ad.









The article is a reprint of material from AUDImanual