Audi A4 Owners & Service Manuals

Audi A4: A/C System Operation

General Information

The temperature in the passenger compartment depends on the amount of heat radiated through the windows and conducted by the metal parts of the body. In hot weather it is possible to achieve a more comfortable temperature for the passengers by pumping off some of the heat.

As heat spreads into cooler areas, the passenger compartment is equipped with a unit for generating low temperatures. In the unit, refrigerant is constantly evaporated. The heat required for this is extracted from the air flowing through the evaporator.

After absorbing heat, the refrigerant is pumped off through the compressor. The action of the A/C compressor increases the heat content and temperature of the refrigerant. Its temperature is then substantially higher than that of the surrounding air.

The warm refrigerant flows to the condenser. There, the refrigerant dissipates its heat through the condenser to the surrounding air due to the temperature difference between the refrigerant and air.

The refrigerant thus acts as a heat transfer medium. As it is to be reused, the refrigerant is returned to the evaporator.

For this reason all air conditioning systems are based on the refrigerant circulation principle. There are however differences in the combination of aggregates.


Being comfortable while driving leads to better concentration and safe driving. Air conditioning makes drivers and passengers more comfortable when temperatures or humidity are high. While opening the windows or sunroof or increasing the air flow can make vehicle occupants more comfortable, it also exposes them to more noise, draughts, exhaust, pollen and dust.

A well-designed heating and air conditioning system can increase comfort by controlling the temperature, humidity and air flow inside the vehicle. This is done both when the vehicle is moving and when it is stationary.

Air conditioning also offers these advantages:

  • It cleans the air that enters the vehicle interior. The damp fins on the evaporator collect dust and pollen, which is then removed by condensation.
  • Temperatures in a mid-size vehicle (for example: after a short drive, outside temperature 30 ºC (86 ºF) in the shade and the vehicle exposed to sunlight).

Environmental Information

Since roughly 1992, the air conditioning systems of newly manufactured cars have been successively converted to refrigerant R134a. This refrigerant does not contain chlorine and does not deplete the ozone layer.

Until roughly 1992, refrigerant R12 was used for air conditioning systems. Due to its chlorine atoms, this CFC has a high potential for depleting the ozone layer as well as a tendency to increase the greenhouse effect.

Conversion programs are available for old existing systems filled with the ozone-depleting substance R12. Refer to Repair Manual for A/C Systems with Refrigerant R12 (this repair manual is only available in hard copy).

The greenhouse potential of R134a (Global Warming Potential = GWP) is approximately 1400, for this reason the European commission has committed that from 01/01/2017 no vehicles with this can newly be brought into the market. Refer to → Chapter "Refrigerant R134a Environmental Information". For this reason from 2016 for new vehicles a refrigerant with a GWP smaller than 150 in introduced (for example the refrigerant R1234yf with a GWP less than 5).

For environmental protection reasons, refrigerants must not be released into the atmosphere. For laws and regulations. Refer to → Chapter "Laws and Regulations".


     General Safety Precautions

    As per VBG 20, German industrial liability insurance association. Pay attention to the workshop-specific instructions. It should be kept in the workshop. Product Characteristics Refrigerants use

     A/C System and Refrigerant R134a Safety Precautions

    Vehicles with a high-voltage system (hybrid vehicles) Extremely Dangerous Due to High-Voltage The high-voltage system is under high-voltage. Electrocution can cause death or very serious personal inj

     Refrigerant Circuit, General Precautions

    General Information Ensure absolute cleanliness when working. Wear safety goggles and gloves when working with refrigerant and nitrogen. Workshop extraction systems are to be switched on. Use th


     Compressor, Replacing on Account of Leakage or Internal Damage

    Vehicles with a High Voltage System (Hybrid Vehicles) Extremely Dangerous Due to High-Voltage The high-voltage system is under high-voltage. Death or serious bodily injury by electric shock. - Individuals with electronic/medical life- and health sustaining machines in or on their person canno

     Service Station, Important Usage Information

    Observe the following with regard to service station operation. Refer to the Parts Catalog (Tools; Special Tools and Equipment: A/C and Heating). - The filters and dryers installed must be replaced at the latest on completion of the service life specified in the relevant operating instructi

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