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Regulation of Automatic air conditioning, function - GF83.40-P-2004CE

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

MODEL 204.3 

MODEL 204.9 

Function requirements, general 

IMPORTANT The circuit status of circuit 15 is provided by the electronic ignition lock control unit (N73) via interior CAN (CAN B).

The "Engine is running" signal is provided by the CDI control unit (N3/9) (with diesel engine) or by the ME-SFI [ME] control unit (N3/10) (with gasoline engine) via chassis CAN (CAN E) and forwarded by the front SAM control unit with fuse and relay module (N10/1) to the automatic climate control and operating unit (N22/7) via interior CAN.

Automatic air conditioning regulation, general 

The electronic control of the temperature and the air distribution in the interior is performed depending on the selected settings at the control and operating unit and the variables measured by various sensors (e.g. interior temperature, outside temperature, coolant temperature, vehicle speed).

The determination of these variables will be described following the description of the settings that are relevant for regulation. The control and operating unit is networked with the vehicle electronics system via interior CAN, climate control LIN (LIN B8) and direct lines. This in turn makes it possible to incorporate relevant parameters in order to improve regulation quality and to lower power consumption.

The automatic air conditioning regulation comprises the following subfunctions:

Function sequence for adjustments that are relevant for regulation 

The function sequence for adjustments that are relevant for regulation comprises the following subfunctions:

Additional function requirements, automatic regulation 

Function sequence for automatic regulation 

The regulation of temperature, air distribution, and air volume takes place depending on the temperature preselection on the control and operating unit and the currently existing basic conditions. The air distribution and air volume are set automatically.

In the process, the control and operating unit takes the following variables into account:

Additional function requirements, manual regulation 

Function sequence for manual regulation 

The regulation of temperature, air distribution, and air volume takes place depending on the temperature selections made on the control and operating unit and the currently existing basic conditions.

The control and operating unit takes the same variables into consideration as with automatic control.

IMPORTANT Pressing the "Mono" button (without code (494) USA version) allows the setting of the temperature preselection for the driver side to be adopted for the other zones (passenger side and rear). For vehicles with code (581) Comfort automatic air conditioning the air distribution currently set on the driver side is also adopted for the passenger side.

Additional function requirements, defroster function 

Function sequence for defroster function 

When the "defrost" button is pressed, all air flaps of the air conditioner housing are closed with the exception of the defroster flaps and the fresh air/recirculated air flap. These are fully opened.

The defroster flaps are adjusted so that the maximum air flow is directed to the windshield and the front side windows. The blend air flaps are set to full warm air supply.

The blower motor (A32m1) is actuated by the control and operating unit via the blower regulator (A32n1) to ensure the best possible defrost mode dependent on the temperature of the air flowing out. The refrigerant compressor is activated in order to ensure that the air flowing out is dried. The air is dried (cooled) and then heated up to the maximum temperature.

IMPORTANT With code (581) Comfort automatic air conditioning, defrosting takes place separately by the left defroster flap actuator motor (M2/8) for the driver and by the right defroster flap actuator motor (M2/9) for the front passenger. Without code (581) Comfort automatic air conditioning, the regulation for the driver and the front passenger takes place together through the defroster flap actuator motor (M2/16).

Additional function requirements for maximum cooling output (with code (494) USA version) 

Function sequence for maximum cooling output (with code (494) USA version) 

Pressing the "MAX A/C" button raises the basic ventilation level to 100%.

Function sequence, determining variables 

The function sequence for determining variables comprises the following subfunctions:

Function sequence for determining the outside temperature 

The outside temperature sensor (B14) measures the outside temperature. The temperature value is read in directly by the front SAM and transmitted via interior CAN to the control and operating unit. The control and operating unit needs this value to reach the desired interior temperature by adjusting the blend air flaps accordingly.

If the vehicle is stationary, the measured temperature can differ considerably from the outside temperature. The outside temperature is therefore only included in the control if the vehicle speed is v ≥20 km/h.

The previously measured temperature is used at speeds of v < 20 km/h and when the ignition is being switched on and off.

Function sequence for determining the interior temperature 

The interior temperature is sensed in the instrument panel area by the interior temperature sensor (B10/4) and is read in directly by the control and operating unit.

On model 204.0/2 with code (414) Electric glass tilting/sliding roof, the interior temperature is also recorded in the roof area by the interior temperature sensor with integrated fan (N70/3b1). The value is read in by the overhead control panel control unit (N70) and sent over the interior CAN to the control and operating unit.

On model 204.0/2 without code (414) Electric glass tilting/sliding roof and on model 204.9, the interior temperature is also recorded by the interior temperature sensor with integrated fan (N70/3b1). The value is read in directly by the control and operating unit. These interior temperature sensors are equipped with one ventilation blower each that draws in the air required for measuring the temperature out of the vehicle interior.

The ventilation blower enables constant circulation at the interior temperature sensors, which ensures a high accuracy of temperature measurement and temperature control that is as independent of the airflow ratios in the interior as possible is achieved.

A mean value is calculated from the measurements from the interior temperature sensors. Together with the value of the outside temperature sensor, the mean value is compared to a characteristics map stored in the control and operating unit and used to control the interior temperature.

The mean value of the interior temperature is maintained by the control and operating unit with a window or door open and thus ensures that the air conditioning system immediately continues to operate with the specified temperature set.

Function sequence for determining the coolant temperature 

The coolant temperature is recorded by the coolant temperature sensor (B11/4). The temperature value is read in by the CDI control unit or ME-SFI control unit and transmitted to the front SAM control unit via the chassis CAN. It transmits the value to the control and operating unit via interior CAN. The value is used to control the blend air flaps and the coolant circulation pump (M13/5) (with code (581) Comfort automatic air conditioning).

In addition, the value is used to regulate the PTC heater booster (R22/3) (with engine 642, 646.8, 651.9).

Function sequence for determining the solar radiation on the vehicle 

The control and operating unit uses the sun sensor (B32/3) to directly record the angle of incidence and the intensity of the solar radiation on the vehicle. The interior temperature and blower speed are adjusted according to the measurements.

In the event of one-sided solar radiation, an adequate temperature difference is set between the left and the right regulated specified temperatures.

Function sequence for determining the vehicle speed 

The vehicle speed is transmitted by the instrument cluster (A1) 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 p < 1.7 bar and p > 30 bar the refrigerant compressor is switched off.

The refrigerant pressure sensor is read in directly by the front SAM control unit and the read in value is sent via 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) (with code (581) Comfort automatic air conditioning) enables the concentration of carbon monoxide (CO) and nitrogen oxide (NOX ) pollutants to be recorded.

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 signals of the interior humidity/temperature sensor are read in by the control and operating unit via climate control LIN.

In vehicles with code (B03) ECO start/stop function, the engine is started as required so that the refrigerant compressor is running and thus fogging of the windshield is prevented.

Function sequence for determining the door status 

The left front door rotary tumbler switch (A85s1), right front door rotary tumbler switch (A85/1s1), left rear door rotary tumbler switch (A85/3s1) (model 204.0/2/9) and right rear door rotary tumbler switch (A85/4s1) (model 204.0/2/9) record the open and closed states at each door. The left front door rotary tumbler switch is read in by the left front door control unit (N69/1) and the right front door rotary tumbler switch by the right front door control unit (N69/2). The rotary tumbler switches of the rear doors (model 204.0/2/9) are read in by the rear SAM control unit with fuse and relay module (N10/2).

The corresponding signals are sent by the control and operating unit over the interior CAN. The control and operating unit retains the current blower output 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 window position 

Each 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 by the right rear door control unit (N69/4) (model 204.0/2/9) and transmitted to the control and operating unit via interior CAN.

Function sequence, determining the sliding roof position (for model 204.0/2 with code (414) Electric glass tilting/sliding roof) or the panoramic sunroof position (with code (413) Panoramic glass sunroof with top sliding sunroof) 

For 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 temperature 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 control by the rear blend air flap actuator motor (M2/35).

Function sequence for determination of VCS status 

Function sequence for AC component actuation 

The AC component actuation function sequence comprises the following subfunctions:

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 power limitation of the blower motor.

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 switch-on request via the interior CAN to the front SAM control unit. This receives the request and actuates the compressor control valve.

IMPORTANT A refrigerant compressor with magnetic clutch is installed in model 204.002/202 as of 1.6.10, and in vehicles for the Economic Commission for Europe (ECE) as of 1.3.11. 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 AC compressor magnetic clutch. This saves fuel. The control and operating unit sends the request to the front SAM control unit via the interior CAN. It actuates the magnetic clutch directly.

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 straight 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.

IMPORTANT With VCS [SBS] active, the blower output is limited.

IMPORTANT The blower output is limited by the control and operating unit on vehicles with code (B03) ECO start/stop function when the engine stops. For this purpose, the control and operating unit receives the status "Engine stop enabled" by the CDI control unit or ME-SFI [ME] control unit via chassis CAN, front SAM control unit and interior CAN.

Function sequence for actuating the PTC heater booster (with engine 642, 646.8 and 651.9) 

In vehicles with engine 642, 646 or 651, the PTC HB is activated via the climate control LIN as required.

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:

Vehicles with code (581) Comfort automatic air conditioning:

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 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.

REFER TO SYSTEM WIRING DIAGRAMS Electrical function schematic for automatic air conditioning, input signals   PE83.40-P-2052-97FAB
REFER TO SYSTEM WIRING DIAGRAMS Electrical function schematic for automatic air conditioning, actuation   PE83.40-P-2053-97FAB
  Overview of automatic climate control system components   GF83.40-P-9995CE
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