Part 2

GF83.40-P-2004CE Regulation of Automatic Air Conditioning, Function
MODEL 204.0 /2 as of model year 2009 /YoM 08
MODEL 204.3
MODEL 204.9

Function sequence for determining the vehicle speed
The vehicle speed is transmitted by the instrument cluster to the control and operating unit via interior CAN. The vehicle speed is used for regulation of the ram air function and for internal calculation of the outside temperature, e.g. in stationary operation.

Function sequence for determining the temperature at the evaporator
To prevent any icing-up of the evaporator, the temperature there is recorded by the evaporator temperature sensor (B10/6) and read in directly by the control and operating unit.
If the evaporator temperature drops to approx. T = 2°C, the refrigerant compressor is switched off.

Function sequence, determining the refrigerant pressure
The refrigerant pressure is recorded by the refrigerant pressure sensor (B12). The pressure is compared with a stored temperature/ pressure curve. At a refrigerant pressure of p<1.7 bar and p > 30 bar the refrigerant compressor is switched off.
The coolant pressure sensor signals are read in directly by the front SAM control unit. The front SAM control unit sends the value read in over the interior CAN to the control and operating unit.

Function sequence for determining the engine speed
The engine speed is registered by the CDI control unit or the ME-SFI [ME] control unit and sent over the chassis CAN to the front SAM control unit. It transmits the value to the control and operating unit via interior CAN.
The engine speed is used among others to regulate the refrigerant compressor.

Function sequence for determining the pollutant concentration of the outside air (with code (581) Comfort automatic air conditioning)
The pollutant sensor (B31) records the following environmental influences:
- Carbon monoxide (CO)
- Nitrogen oxides (NOx)
- Outside dew point temperature
- Relative humidity
- Ambient temperature
The values are read in directly by the control and operating unit over the climate control LIN. The control and operating unit controls the automatic recirculation according to the read-in values.

Function sequence for determining dew point temperature (with code (581) Comfort automatic air conditioning up to 31.5.10)
The ambient temperature and air humidity are used by the dew point sensor (B11/12) (with code (581) Comfort automatic air conditioning up to 31.5.10) to calculate the dew point and it then sends this over the climate control LIN to the control and operating unit.
When the dew point is reached, the windows and the outside mirrors start to fog up. To prevent this, the air conditioning, the heated outside mirror and the heated rear window are activated.

Function sequence for determining temperature and moisture of windshield (as of 1.12.09)
The interior humidity/temperature sensor (B82) measures the relative humidity and temperature directly at the inside of the windshield and uses this to determine the dew point temperature.
The interior humidity/temperature sensor signals are read in by the control and operating unit over the climate control LIN.
If the windows threaten to fog up, corresponding countermeasures are taken such as, e.g. switching on the refrigerant compressor or starting the engine (with code (B03) ECO start/stop function).

Function sequence for determining the door status
The left front door rotary tumbler switch (A85s1) in the left front door lock (A85), the right door rotary tumbler switch (A85/1s1) in the right front door lock (A85/1), the left rear door rotary tumbler switch (A85/3s1) in the left rear door lock (A85/3) (model 204.0/2/9) and the right rear door rotary tumbler switch (A85/4s1) in the right rear door lock (A85/4) (model 204.0/2/9) record the states of open or closed at each of the doors.
The status of the left front door rotary tumbler switch is read in by the left front door control unit (N69/1) and the status of the right front door rotary tumbler switch is read in by the right front door control unit (N69/2). The status of the rear door rotary tumbler switches (model 204.0/2/9) is read in by the rear SAM control unit with fuse and relay module (N10/2).
The status of each door is sent over the interior CAN to the control and operating unit. The control and operating unit retains the current blower setting when the door is open in order to prevent unnecessary readjustment in the event of high temperature differences between the inside and outside air.

Function sequence for determining the side window position
Each side window position is read in by the left front door control unit, right front door control unit, left rear door control unit (N69/3) (model 204.0/2/9) and the right rear door control unit (N69/4) (model 204.0/2/9) and sent over the interior CAN to the control and operating unit.

Function sequence for determining tilting/sliding roof position (in model 204.0/2 with code (414) Power glass tilting/sliding roof) or the panoramic sunroof position (with code (413) Panoramic glass sunroof with top sliding sunroof)
In model 204.0/2 with code (414) Electric glass tilting/sliding roof, the position of the tilting/sliding roof is read in by the overhead control panel control unit and sent over the interior CAN to the control and operating unit. With code (413) Panoramic glass sunroof with top sliding sunroof, the position of the panoramic glass sunroof is read in by the panoramic sliding sunroof control unit (A98) and sent via interior CAN to the control and operating unit.

Function sequence for determining settings on rear automatic air conditioning operating unit (with code (581) Comfort automatic air conditioning)
The rear compartment climate control functions can be adjusted by the rear passengers using the rear automatic air conditioning control unit.
Operating the rockers for temperature and blower setting in the rear automatic air conditioning operating unit is read in and processed over the climate control LIN by the control and operating unit. This data is used to actuate or regulate the air volume of the rear vents through the rear blower motor (M2/1) and the rear temperature by the rear blend air flap actuator motor (M2/35).

Function sequence for determination of VCS status
With VCS [SBS] active, the blower output is limited.
The radio with auto pilot system (A2/56) (with code (511) Audio 50 APS incl. DVD changer or the COMAND controller unit (A40/3) (with code (512) COMAND APS with DVD changer or with code (527) COMAND APS with single DVD drive (with navigation)) sends the voice control system status over the interior CAN to the control and operating unit. The control and operating unit forwards the request directly to the blower regulator, which then undertakes the output limitation of the blower motor.

Function sequence for AC component actuation
The function sequence for actuating the A/C components encompasses the following subfunctions:
^ Function sequence for actuation of refrigerant compressor
^ Function sequence for actuation of blower motor
^ Function sequence, actuation of the PTC heater booster (for diesel engine)
^ Function sequence for actuation of the air ducting flaps
^ Function sequence for actuation of combustion engine fan motor and air conditioning with integrated control (M4/7)
^ Function sequence for actuation of coolant circulation pump (with code (581) Comfort automatic air conditioning or code (B03) ECO start/stop function)
^ Function sequence for actuation of rear blower motor (with code (581) Comfort automatic air conditioning)

Function sequence for actuation of refrigerant compressor
The refrigerant compressor is responsible for induction and compression of the refrigerant. The refrigerant compressor output is regulated continuously from 0 to 100 % by the control and operating unit over the compressor control valve.
The control and operating unit transmits the actuation request over the interior CAN to the front SAM control unit. This receives the request and actuates the compressor control valve accordingly.
The control and operating unit also sends the request for idle speed increase over the interior CAN to the front SAM control unit.
This receives the request and sends it over the chassis CAN to the ME-SFI [ME] control unit or the CDI control unit. This increases the idle speed to match the corresponding load applied when the refrigerant compressor was switched on.
In vehicles with code (B09) Refrigerant compressor with magnetic clutch a refrigerant compressor with magnetic clutch is installed. To prevent the refrigerant compressor from turning with the air conditioning switched off, the belt pulley is disconnected from the drive shaft of the refrigerant compressor by means of the magnetic clutch. This saves fuel. The control and operating unit sends the request to the front SAM control unit via the interior CAN. This directly actuates the magnetic clutch.

Function sequence for actuation of blower motor
Ventilation is achieved with the aid of the blower motor. The control and operating unit forwards the request directly to the blower regulator, which then actuates the blower motor.
With code (581) Comfort automatic air conditioning, the ventilation of the rear passenger compartment is also supported by the rear blower motor. Actuation is performed by the control and operating unit via the climate control LIN.
With VCS [SBS] active, the blower output is limited.
The blower output is limited by the control and operating unit on vehicles with code (B03) ECO start/stop function when the engine stops. To this end, the control and operating unit sends the "Engine stop approved" status from the CDI control unit or the ME-SFI [ME] control unit over the chassis CAN, front SAM control unit and the interior CAN.

Function sequence, actuation of the PTC heater booster (for diesel engine)
When required (e.g.for a cold start) the PTC heater booster is activated through the climate control LIN by the control and operating unit.

Function sequence for actuation of the air ducting flaps
The air distribution in the vehicle interior is controlled by corresponding adjustment of the air duct flaps in the air conditioning housing.
The control and operating unit actuates the following components over the climate control LIN:
Vehicles without code (581) Comfort automatic air conditioning:
- for fresh air/recirculated air control:
- Fresh air/recirculated air flap actuator motor (M2/5)
- for temperature control:
- Left blend air flap actuator motor (M2/6)
- Right blend air flap actuator motor (M2/7)
- for ventilation control:
- Defroster flap actuator motor
- Air distribution flap actuator motor (M16/22)
Vehicles with code (581) Comfort automatic air conditioning:
- for fresh air/recirculated air control:
- Fresh air/recirculated air flap actuator motor
- for temperature control:
- Left blend air flap actuator motor
- Right blend air flap actuator motor
- Rear blend air flap actuator motor (M2/35)
- for ventilation control:
- Left defroster flap actuator motor
- Right defroster flap actuator motor
- Left footwell flap actuator motor (M2/10)
- Right footwell flap actuator motor (M2/11)
- Left center air vent flap actuator motor (M2/12)
- Right center air vent flap actuator motor (M2/13)
- Diffuser flap actuator motor (M2/21)
- For ram air control:
- Ram air flap actuator motor (M2/34) (in model 204.0/2 up to 31.5.10)
- Fresh air/recirculated air flap actuator motor (in model 204.0/2 as of 1.6.10)

Function sequence for actuation of combustion engine fan motor and air conditioning with integrated control
The fan motor is used for cooling the coolant and refrigerant.
The control and operating unit calculates the specified fan speed depending on the refrigerant pressure and transmits the request to the front SAM control unit over the interior CAN. This sends the request to the CDI control unit or to the ME-SFI [ME] control unit over the chassis CAN.
The CDI control unit or the ME-SFI [ME] control unit then calculates the target fan speed depending on the engine temperature and compares this with the request from the control and operating unit. The fan motor is then actuated with a pulse width modulation (PWM) signal by the CDI control unit or ME-SFI [ME] control unit.

Function sequence for actuation of coolant circulation pump (with code (581) Comfort automatic air conditioning or code (B03) ECO start/stop function)
The coolant circulation pump is used to support the coolant circuit, e.g. at low engine speeds, when the engine is stopped (with code (B03) ECO start/stop function) or when the residual-heat utilization function is used. The control and operating unit sends the request for actuation of the coolant circulation pump over the interior CAN to the front SAM control unit. This then directly actuates the coolant circulation pump.

Function sequence for actuation of rear blower motor (with code (581) Comfort automatic air conditioning)
The rear blower motor is also used to ventilate the rear compartment. The rear blower motor is actuated via climate control LIN by the control and operating unit.