Automatic air conditioning, function - GF83.40-P-0005CE

MODEL 204.0/2 as of model year 2009/YoM 08 

Fig 1: Automatic Air Conditioning Function Diagram

Courtesy of MERCEDES-BENZ USA

Function requirements, general 

• Control functions: Circuit 15
• Climate control: Circuit 61

The electronic ignition lock control unit (N73) transmits the circuit status of circuit 15 to the interior CAN (CAN B). The circuit status of circuit 61 is provided by the CDI control unit (N3/9) (with diesel engine) or ME-SFI [ME] control unit (N3/10) (with gasoline engine) on the chassis CAN (CAN E) and forwarded by the front SAM control unit with fuse and relay module (N10/1) via interior CAN to the automatic air conditioning control and operating unit (N22/7).

Automatic air conditioning, general 

2 different automatic air conditioning versions are installed:

• Automatic air conditioning with 2-zone temperature control (without code (581) Comfort automatic air conditioning)
• Automatic air conditioning with 3-zone temperature control (with code (581) Comfort automatic air conditioning)

Regulation and control are performed by the control and operating unit.

The automatic air conditioning without code (581) Comfort automatic air conditioning is equipped with a separate temperature control for the left and the right half of the vehicle.

Blower control takes place with 1 zone and can be operated manually or controlled automatically.

The automatic air conditioning with code (581) Comfort automatic air conditioning is equipped with a separate temperature control for the left and the right half of the vehicle and for the rear compartment.

The front blower control can be manually or automatically operated. In the rear, only manual operation is possible using the separate rear automatic air conditioning operating unit (N22/4) (with code (581) Comfort automatic air conditioning).

The blower is controlled in 2 zones (front and rear)

The automatic air conditioning comprises the following subfunctions:

• Heating circuit function sequence 
• Function sequence for residual engine heat utilization (with code (581) Comfort automatic air conditioning without code (494) USA version) 
• Function sequence for evaporator drying process 

Further subfunctions are described in separate sections:

• Automatic air conditioning refrigerant circuit, function 
• Ventilation system, function 
• Regulation of Automatic air conditioning, function 

Heating circuit function sequence 

Driven by the coolant pump, the coolant circulates in the engine cooling circuit. In the process, it absorbs engine heat. The heated coolant passes through the heater heat exchanger, which dissipates heat to the air blowing by.

At lower engine speeds, the coolant circulation pump (M13/5) (with code (581) Comfort automatic air conditioning) is also activated to ensure that the flow rate required to heat up the air flowing past is achieved.

The coolant circulation pump is actuated by the front SAM control unit on request of the control and operating unit.

Function sequence for residual engine heat utilization (with code (581) Comfort automatic air conditioning without code (494) USA version) 

The function is switched on when the "REST" button on the control and operating unit is pressed. The control and operating unit transmits the request via the interior CAN to the front SAM control unit, which directly actuates the coolant circulation pump. The coolant circulation pump delivers the still warm (residual heat) coolant through the heat exchanger.

At the same time, the control and operating unit sends the ventilation request to the blower regulator (A32n1), which then actuates the blower motor (A32m1) at reduced power. The air drawn in by the blower motor is routed along the heater heat exchanger and thus heated up.

The function is terminated after a specified fixed time or when the on-board power supply voltage drops below a certain value.

Additional function requirements for evaporator drying process 

• Air conditioning was active at least once during the ignition sequence
• Evaporator temperature T > 3 °C
• Engine OFF (circuit 61 OFF)
• Doors closed
• Kilometer reading > 250 km

Function sequence for evaporator drying process 

To counteract any evaporator odor in the interior and any fogging of windows when starting the air conditioning, an evaporator drying process on the air conditioning system is conducted.

At circuit 61 Off the timer in the instrument cluster (A1) is activated.

The circuit status is read in by the CDI control unit or by the ME-SFI [ME] control unit over the chassis CAN and sent to the instrument cluster.

After a waiting time of t = 1 h the instrument cluster sends the request for the evaporator drying process via the interior CAN to the control and operating unit which then starts the evaporator drying process. To this end the blower is activated at the lowest setting for t = 30 min.

The control and operating unit transmits the request from the blower directly to the blower regulator. The blower regulator actuates the blower motor at the lowest blower stage.