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

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

MODEL 204.3

MODEL 204.9

Fig 1: Identifying Automatic Air Conditioning Function Diagram

Courtesy of MERCEDES-BENZ USA

Function requirements, general

Control functions: circuit 15
Climate control: Engine is running

The circuit 15 status is provided by the electronic ignition lock control unit via interior CAN. The "Engine is running" signal is provided by the CDI control unit or by the ME-SFI [ME] control unit via chassis CAN and forwarded to the control and operating unit by the front SAM control unit via interior CAN.

Automatic air conditioning general

Two 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. Manual operation is only possible in the rear using a separate rear automatic air conditioning operating unit.

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 documents:

Automatic air conditioning refrigerant circuit, function
Ventilation system, function
Regulation of Automatic air conditioning, function
Heated rear window, 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.

Additionally, at low engine rpm, the coolant circulation pump is actuated to ensure that the flow volume needed to heat up the air flowing past is adequate.

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 over 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, which then actuates the blower motor 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
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 is conducted at the air conditioning system.

When the engine is turned off, the timer is activated in the instrument cluster. The "Engine off" signal 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.

	Automatic air conditioning refrigerant circuit, function		GF83.40-P-2005CE
	Ventilation system, function		GF83.10-P-2000CE
	Regulation of Automatic air conditioning, function		GF83.40-P-2004CE
	Heated rear window, function		GF67.29-P-0003CE