Automatic air conditioning refrigerant circuit, function

P83.40-3929-79

Function requirements, general

 Engine running

 Automatic air conditioning switched on

Automatic air conditioning refrigerant circuit, general

Control of the automatic air conditioning refrigerant circuit is performed by the automatic air conditioning control and operating unit (N22/7). The air in the vehicle interior is cooled depending on the setting on the automatic air conditioning control and operating unit or rear automatic air conditioning operating unit (N22/4) (with code (581) Comfort automatic air conditioning) by the automatic air conditioning refrigerant circuit.

The automatic air conditioning refrigerant circuit mainly consists of the following components:

 Refrigerant compressor

 Condenser

 Accumulator (drier)

 Expansion valve

 Evaporator

The individual components of the refrigerant circuit are interconnected through hoses and pipelines and form a closed system.

The automatic air conditioning refrigerant circuit function consists of the following functional components:

 High-pressure side

 Low-pressure side

 The separation points for this are the valve plate at the refrigerant compressor and the injection valve at the expansion valve.

High-pressure side

The refrigerant compressor driven by the engine draws in the cold gaseous refrigerant from the evaporator, compresses it, whereby it is heated, and delivers it to the condenser. The compressed hot refrigerant is cooled in the condenser by the outside air flowing past. On reaching the pressure-specific dew point temperature, the refrigerant condenses and changes in terms of its physical state from gaseous to fluid. The completely liquefied refrigerant then flows into the fluid reservoir (drier). While it is flowing through the fluid reservoir, moisture is removed from the refrigerant and any chemical or mechanical impurities are filtered out in order to protect the downstream components from these. The cleaned refrigerant then flows to the expansion valve. The liquid refrigerant, which is under high pressure, is injected into the evaporator.

 The refrigerant pressure is measured by the refrigerant pressure sensor.

Low-pressure side

The liquid refrigerant decompresses in the evaporator and changes again in terms of its physical state from fluid to gaseous. The evaporation heat required for the evaporation is removed from the air flowing past at the evaporator fins, cooling it down in the process. The refrigerant, which is completely gaseous once more, is drawn in and compressed by the refrigerant compressor.

 As of 1.12.09 on model 207.3 and on model 207.4, a coaxial heat exchanger is installed. This increases the output and efficiency of the refrigerant circuit.

 To prevent the evaporator from icing up, the refrigerant compressor is switched off by the AAC control and operating unit if the temperature drops below a specific value at the evaporator. The evaporator temperature is recorded by the evaporator temperature sensor.