Automatic air conditioning refrigerant circuit, function - GF83.40-P-2005FL

MODEL 212 (except 212.095/098/298) 

Fig 1: Automatic Air Conditioning Refrigerant Flow Diagram - Model 212 (Except 212.095/098/298)

Courtesy of MERCEDES-BENZ USA

Function requirements, general 

• Engine running
• Automatic air conditioning switched on

Automatic air conditioning refrigerant circuit, general 

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

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 refrigerant circuit is split up as follows:

• High-pressure side 
• Low-pressure side 

The connecting 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 flow of outside air that has been drawn in by the internal combustion engine and air conditioning system fan motor with integrated control (M4/7). On reaching the dew point dependent on the pressure, the refrigerant condenses and changes in terms of its physical state from gaseous to fluid.

The refrigerant then flows into the accumulator (drier). While it is flowing through the fluid reservoir, moisture is removed from the refrigerant, vapor locks are separated and any 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.

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 again and compressed by the refrigerant compressor.

The cooled air is routed to the vehicle interior.

As of 1.12.09 a coaxial heat exchanger will be installed. This increases the cooling output.

To prevent the evaporator from icing up, the refrigerant compressor is switched off by the 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.