GF83.40-P-2004GM Regulation of Automatic Air Conditioning, Function
GF83.40-P-2004GM Regulation Of Automatic Air Conditioning, Function
Function requirements, general
^ Circuit 15 On
^ Automatic air conditioning switched on
^ Circuit 61 ON (for cooling mode)
^ Refrigerant compressor (A9) switched on (for cooling mode)
The circuit status of circuit 15 is provided by the EIS [EZS] control unit (N73) on the interior CAN (CAN-B).
Automatic air conditioning regulation, general
The electronic regulation of the temperature and the air distribution in the interior compartment takes place depending on the settings selected on the AAC [KLA] control and operating unit (N22) (without code (581) Comfort automatic air conditioning) or on the comfort AAC [KLA] control and operating unit (N22/7) (with code (581) Comfort automatic air conditioning) and the variables measured by various sensors (e.g. outside temperature, interior temperature, coolant temperature).
The determination of these variables is described following the description of the adjustments that are relevant for regulation.
The control and operating unit is networked with the vehicle electronics system via the interior CAN, the 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, recording of adjustments that are relevant for regulation
^ Function sequence, determining variables
^ AC component actuation function sequence
Function sequence, recording of adjustments that are relevant for regulation
The function sequence for adjustments that are relevant for regulation comprises the following subfunctions:
^ Function sequence for automatic regulation
^ Function sequence with manual regulation
^ Function sequence of defroster function
Additional function requirements, automatic regulation
^ AUTO button pressed (LED lights up)
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:
- Ambient temperature
- Interior temperature
- Coolant temperature
- Temperature at the air outlets in the vehicle
- Solar radiation on the vehicle
- Vehicle speed
- Temperature on evaporator
- Temperature at rear air conditioning evaporator
(with code (582) Rear air conditioning)
- Refrigerant pressure
- Engine speed
- Pollutant concentration of the outside air (with code (581) Comfort automatic air conditioning)
- Dew point temperature (with code (581) Comfort automatic air conditioning)
- Door status and liftgate status
- Window position
- Tilting/sliding roof position (with code (414) Electric glass tilting/ sliding roof) or panoramic sunroof position (model 251 with code (413) Panoramic glass sunroof with top sliding sunroof)
- Vent window position (model 164.8 and model 251 with code (848) Electric side vent window)
- Settings on the RCP [HBF] control unit (N72/2)
- Status of voice control system (VCS [SBS]) (as of 1.7.09 with code (511)) Audio 50 APS with DVD changer or with code (512) COMAND APS with DVD changer or with code (527) COMAND APS with single DVD drive (with navigation))
Additional function requirements, manual regulation
^ Air distribution and air volume changed manually (LED in AUTO button does not light up)
Function sequence with 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.
Additional function requirements, defroster function
^ Defroster button pressed (light emitting diode lights up)
Function sequence of defroster function
When the defroster button is pressed, all air flaps are closed with the exception of the defroster flaps and the fresh air/air recirculation flap. These are fully opened.
The defroster and side air vents are adjusted so that the maximum air flow is directed to the windshield and the front side windows. 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.
With code (581) Comfort automatic air conditioning, defrosting takes place separately through the left defroster flap actuator motor (M2/8) for the driver and 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 left and right defroster flaps actuator motor (M2/16).
Function sequence, determining variables
The function sequence for determining variables comprises the following subfunctions:
^ Function sequence, determining the outside temperature
^ Function sequence, determining the interior temperature
^ Function sequence, determining the coolant temperature
^ Function sequence, determining the temperature at the air outlets in the vehicle
^ Function sequence, determining the vehicle speed
^ Function sequence, determining the solar radiation on the vehicle
^ Function sequence, determining the temperature on the evaporator and on the rear air conditioning evaporator (with code (582) Rear air conditioning)
^ Function sequence, determining the refrigerant pressure
^ Function sequence, determining the engine speed
^ Function sequence for determining the pollutant concentration of the outside air (with code (581) Comfort automatic air conditioning)
^ Function sequence for determining dew point temperature (with code (581) Comfort automatic air conditioning)
^ Function sequence, determining the door status and liftgate status
^ Function sequence, determining the window position
^ Function sequence, determining the tilting/sliding roof position (with code (414) Electric glass tilting/sliding roof) or the panoramic sunroof position (model 251 with code (413) Panoramic glass sunroof with top sliding sunroof)
^ Function sequence, determining the vent window position (model 164.8 and model 251 with code (848) Electric side vent window)
^ Function sequence, determining the settings on the RCP [HBF] control unit
^ Function sequence for determining the voice control system status (as of 1.7.09)
Function sequence, determining the outside temperature
The outside temperature indicator temperature sensor (B14) measures the outside temperature. The temperature value is read in directly by the control and operating unit.
Function sequence, determining the interior temperature
The interior temperature is measured by the in-car temperature sensor (N22b1) (without code (581) Comfort automatic air conditioning) or the In-car temperature sensor (N22/7b1) (with code (581) Comfort automatic air conditioning) in the control and operating unit.
The in-car temperature sensor is equipped with an aspirator blower which draws in air required for the temperature measurement out of the vehicle interior.
The aspirator blower ensures that the vehicle interior air is constantly circulated at the in-car temperature sensor and thus ensures a high degree of control accuracy.
By means of the in-car temperature sensor, a temperature control is achieved which is largely independent of the air flow conditions in the interior compartment.
Function sequence, determining the coolant temperature
The temperature of the coolant is registered by the coolant temperature sensor (B11/4). The temperature value is read by the CDI control unit (N3/9) (for diesel engines) or by the ME-SFI [ME] control unit (N3/10) (for gasoline engines) and transmitted to the central gateway control unit (N93) over the engine compartment CAN (CAN C). It transmits the value to the control and operating unit via interior CAN.
The value is used to control the blend air flaps, to regulate the PTC heater booster (R22/3) (for diesel engines) and to actuate the heater circulation pump (M13).
Function sequence, determining the temperature at the air outlets in the vehicle
The temperature at the air outlets is recorded by the following sensors:
- Center rear interior temperature sensor (B10/7)
- Left side air vent air outlet temperature sensor (B10/31)
- Right side air vent air outlet temperature sensor (B10/32)
- Left center outlet temperature sensor (B10/33)
- Right center outlet temperature sensor (B10/34)
- Left footwell air outlet temperature sensor (B10/35)
- Right footwell air outlet temperature sensor (B10/36)
- Rear headroom AC temperature sensor (B10/37)
(with code (582) Rear air conditioning)
The control and operating unit regulates the outlet air temperature at the respective air outlets.
The temperature sensors are read in directly by the control and operating unit.
Function sequence, 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 the internal calculation of the outside temperature, e.g. during operation while standing.
Function sequence, determining the solar radiation on the vehicle
The sun sensor (B32) (without code (581) Comfort automatic air conditioning) measures the intensity of the solar radiation acting on the vehicle using photo diodes.
The dual sun sensor (B32/3) (with code (581) Comfort automatic air conditioning) registers intensity and angle of incidence of the solar radiation on the vehicle. The dual sun sensor differentiates between left and right solar incidence, in other words it has two photodiodes.
The measurement values are registered directly by the control and operating unit, and the interior temperature and the blower speed are adjusted accordingly.
Function sequence, determining the temperature on the evaporator and on the rear air conditioning evaporator
To prevent the evaporator and the rear air conditioning evaporator from icing up, their temperature is measured by the evaporator temperature sensor (B10/6) and the rear air conditioning evaporator temperature sensor (B10/11) (with code (582) Rear air conditioning) and read in directly by the control and operating unit. If the evaporator temperature drops to approx. T = 2 °C, the refrigerant compressor or the rear air conditioning refrigerant shutoff valve (Y67) (with code (582) Rear air conditioning) is switched off.
Function sequence, determining the refrigerant pressure
The refrigerant pressure is measured by the refrigerant pressure sensor (B12) and compared to a temperature/pressure curve stored in the control and operating unit. At a certain value, the refrigerant compressor is switched off.
The refrigerant pressure sensor is read in directly by the control and operating unit.
Function sequence, determining the engine speed
The engine speed is registered by the CDI control unit or the MESFI [ME] control unit and transmitted to the central gateway control unit via engine compartment CAN. It transmits the value to the control and operating unit via interior CAN.
The engine speed value is used to regulate the refrigerant compressor, among other things.
Function sequence for determining the pollutant concentration of the outside air (with code (581) Comfort automatic air conditioning)
The pollutant sensor (B31) measures the concentration of the pollutants carbon monoxide (CO) and nitrogen oxide (NO X).
The values are read in directly by the comfort AAC control and operating unit. The comfort AAC 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)
The dew point sensor (B11/12) uses the ambient temperature and the air humidity to calculate the dew point and transmits it to the comfort AAC control and operating unit via climate control LIN. When the dew point is reached, the windows and the outside mirrors start to fog up. In order to prevent this, the air conditioning system and the heated outside mirror are activated by the comfort AAC control and operating unit.
Function sequence, determining the door status and liftgate status
The right front door rotary tumbler microswitch (M14/5s1), left front door rotary tumbler microswitch (M14/6s1), left rear door rotary tumbler microswitch (M14/8s1) and the right rear door rotary tumbler microswitch (M14/9s1) register the open or closed status of the relevant door.
The rear-end door locking unit (A72) registers the condition open or closed of the liftgate.
The door status and the liftgate status are read in by the rear SAM control unit (N10/8) and transmitted to the control and operating unit.
The control and operating unit retains the current blower output when the door or liftgate is open in order to prevent unnecessary readjustment in the event of high temperature differences between the inside and outside air.
Function sequence, determining the window position
The left front window position is read in by the left front door control unit (N69/1), the right front window position by the right front door control unit (N69/2) and the particular rear window position by the front SAM control unit (N10) and transmitted to the control and operating unit.
Function sequence, determining the tilting/sliding roof position or the panoramic sunroof position (with code (414) Electric glass tilting/sliding roof) or the panoramic sunroof position (model 251 with code (413) Panoramic glass sunroof with top sliding sunroof)
The position of the tilting/sliding roof or the panoramic sunroof is read in by the overhead control panel control unit (N70) and transmitted to the control and operating unit.
Function sequence, determining the vent window position (Model 164.8 and model 251 with code (848) Electric side vent window)
The position of the vent windows is recorded by the rear SAM control unit on the basis of the signals from the left vent window motor (M21/8) and the right vent window motor (M21/9). The rear SAM control unit forwards the status to the control and operating unit via the interior CAN.
Function sequence, determining the settings on the RCP [HBF] control unit
The rear compartment climate control functions can be adjusted by the rear passengers via the RCP [HBF] control unit. The settings in the RCP [HBF] control unit are read in by the control and operating unit via interior CAN and processed.
Function sequence for determining the voice control system status (as of 1.7.09)
The radio and navigation unit (A2/56) (with code (511) Audio 50 APS with DVD changer) or the COMAND operating, display and controller unit (A40/3) (with code (512) COMAND APS with DVD changer or with code (527) COMAND APS with single DVD drive (with navigation)) transmits the status of the VCS [SBS] to the control and operating unit via the interior CAN.
AC component actuation function sequence
The AC component actuation function sequence comprises the following subfunctions:
^ Function sequence, actuation of the refrigerant compressor
^ Function sequence, actuation of blower motor
^ Function sequence, actuation of the PTC heater booster
^ Function sequence, actuation of the air ducting flaps
^ Function sequence for actuation of engine and air conditioning electric suction fan with integrated control (M4/7)
Function sequence, actuation of the refrigerant compressor
The refrigerant compressor is responsible for induction and compression of the refrigerant. The refrigerant compressor output is regulated continuously up to 100 % by the control and operating unit via the compressor control valve. The control and operating unit transmits the switch on requests directly to the compressor control valve.
Function sequence, actuation of blower motor
Ventilation is achieved with the aid of the blower motor. The control and operating unit transmits an actuation of 0 to 100 % to the blower regulator via the climate control LIN. Depending on the control voltage, the blower regulator regulates the operating voltage for the blower motor from U = 0 V up to U = 12 V and thus the rotational speed of the blower motor from 0 up to 100 %.
As of 1.7.09, the blower output is limited with an active VCS SBS].
The actuation (operating voltage) of the blower motor is influenced by the following factors:
- Blower selector wheel setting ("MANUAL"/"AUTO")
- "AC OFF" (On/Off)
- Mode (heating/cooling)
- Coolant temperature
- Vehicle speed
- Solar radiation
- Fresh air/air recirculation flap position
- Ambient temperature
- Flap positions
- Circuit 15 On (blower ON), circuit 50 On (starter running, blower off)
- Window, tilting/sliding roof, panoramic sunroof position
- Vent windows position
- Air humidity (dew point
(with code (581) Comfort automatic air conditioning)
- Pollutant concentration
(with code (581) Comfort automatic air conditioning)
- Residual engine heat utilization function
- Variant coding
The blower output can be increased to match the outside temperature.
To keep the interior temperature constant and the windows clear at low temperatures, the blower output is increased by 15 % at outside temperatures of T = -10 °C to -15 °C.
With code (581) Comfort automatic air conditioning without code (582) Rear air conditioning, the ventilation of the rear compartment is supported by the booster blower motor (M2/1). The actuation is carried out by the comfort AAC control and operating unit directly at the booster blower electronic blower regulator (N29/2). This directly actuates the booster blower motor.
With code (582) Rear air conditioner, ventilation of the rear compartment is assisted by the rear air conditioning system blower motor (M2/29). Actuation is carried out by the comfort AAC control and operating unit via the climate control LIN at the rear air conditioning system blower regulator (N29/7). This then actuates the rear air conditioning system blower motor directly.
Function sequence, actuation of the PTC heater booster
In vehicles with diesel engine, the PTC heater booster is activated via climate control LIN if required.
Air ducting flaps actuation function sequence
The control and operating unit actuates the following components for adjustment of the air ducting flaps via climate control LIN:
Vehicles without code (581) Comfort automatic air conditioning:
- for fresh air/recirculated air control:
- Fresh air/air recirculation 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:
- Rear shutoff flap actuator motor (M2/12)
- Left and right footwell flaps actuator motor (M2/15)
- Left and right defroster flaps actuator motor
- Rear air distribution flap actuator motor (M2/21)
- Center vent flap actuator motor (M2/22)
Vehicles with code (581) Comfort automatic air conditioning:
- for fresh air/recirculated air control:
- Fresh air/air recirculation flap actuator motor
- for temperature control:
- Left blend air flap actuator motor
- Right blend air flap actuator motor
- 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)
- Rear shutoff flap actuator motor
- Center vent flap actuator motor
- Left center air flap actuator motor (M16/23)
- Right center air flap actuator motor (M16/24)
Function sequence for actuation of engine and air conditioning electric suction fan with integrated control
The electric suction fan serves to cool 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 central gateway control unit via interior CAN.
This transmits the request to the CDI control unit or the ME-SFI [ME] control unit via engine compartment CAN. The CDI control unit or the ME-SFI [ME] control unit calculates the target blower speed depending on the engine temperature and compares it with the air conditioning request. The electric suction fan is then actuated accordingly by the CDI control unit or the ME-SFI [ME] control unit.
