GF83.40-P-2004LEH Regulation of Automatic Air Conditioning, Function
GF83.40-P-2004LEH Regulation Of Automatic Air Conditioning, Function
Function requirements, general
^ Circuit 15 ON (operational functions, heater, ventilation)
^ Circuit 61 ON (cooling)
^ Automatic air conditioning switched on
^ Electric refrigerant compressor (A9/5) switched on (for cooling mode)
^ High-voltage supply error-free
Status of circuit 15 is provided by EIS [EZS] control unit (N73) via interior CAN (CAN B).
The status of circuit 61 is provided by the ME-SFI [ME] control unit (N3/10) via chassis CAN (CAN E) and forwarded from central gateway control unit (N93) via interior CAN to AAC [KLA] control unit (N22/1).
Circuit 61 is required to start the electric refrigerant compressor. Then cooling is possible even without engine speed stop mode).
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 at the upper control panel control unit (N72/1), at the front central operating unit (A40/9) or at the rear air conditioning control unit (N22/4) (with code (582) Rear 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 regulation and control are performed by the AAC [KLA] control unit. This is networked with the vehicle electronics system via the interior CAN, the climate control LIN (LIN B8), the A/C bus (KB) 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 function comprises the following subfunctions:
^ Function sequence, adjustments that are relevant for regulation
^ Function sequence, determining variables
^ AC component actuation function sequence
Function sequence, 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
^ Function sequence, maximum cooling output
(with code (494) USA version)
Additional function requirements, automatic regulation
^ Automatic air conditioning activated by:
- Left automatic air conditioning button (N72/1s33) or right automatic air conditioning button (N72/1s42) in the upper control panel control unit (LED lights up) or
- Front central operating unit or
- Function mode button in the rear air conditioning control unit
Function sequence for automatic regulation
The temperature, the air distribution and the air volume are regulated depending on the temperature preselection at the upper control panel control unit, at the front central operating unit or at the rear air conditioning control unit and the prevailing general conditions. The air distribution and air volume are set automatically.
The following variables are taken into account by the AAC [KLA] control unit:
- Ambient temperature
- Interior temperature
- Coolant temperature
- Temperature at the air outlets in the vehicle
- Solar radiation on the vehicle
- Vehicle speed
- Temperature on the evaporator and on the rear air conditioning evaporator (with code (582) Rear air conditioning)
- Temperature downstream of the rear air conditioning heater heat exchanger (with code (582) Rear air conditioning)
- Refrigerant pressure
- Engine speed
- Pollutant concentration of outside air
- Dewpoint temperature
- Door status
- Window position
- Tilting/sliding roof (SHD) position (with code (414) Power glass tilting/sliding roof) or Panoramic sliding sunroof position (with code (413) Panoramic glass sunroof with top sliding sunroof)
- Status of voice control system (VCS [SBS])
- Settings at upper control panel control unit, at front central operating unit or at rear air conditioning control unit (with code (582) Rear air conditioning)
Additional function requirements for manual regulation
^ Air distribution manually changed by:
- Front central operating unit or
- Air distribution buttons in rear air conditioning control unit
^ Air volume manually changed by:
- Left blower button (N72/1s35) or right blower button (N72/1s40) in upper control panel control unit or
- Front central operating unit or
- Air volume button in rear air conditioning control unit
Function sequence with manual regulation
The temperature, the air distribution and the air volume are regulated depending on the settings made at the upper control panel control unit, at the front central operating unit or at the rear air conditioning control unit and the prevailing general conditions. In this case, some of the same variables as for the automatic regulation are taken into account by the AAC [KLA] control unit.
Additional function requirements, defroster function
^ Defroster function activated by defrost/heated windshield button (N72/1s36) at upper control panel control unit (LED lights up)
Function sequence of defroster function
Pressing the defrost/heated windshield button in the upper control panel control unit closes all air flaps except for the defroster flaps and the fresh air 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. When the coolant is cold, the air volume is reduced.
The air conditioning water valve (Y19/2) is opened and the heater circulation pump (M13) actuated.
The blower motor (A32m1) is actuated by the AAC [KLA] control unit via the blower regulator (A32n1) to ensure the best possible defrost mode dependent on the temperature of the air flowing out. The electric refrigerant compressor is activated in order to extract moisture from the outflowing air. The air is dried (cooled) and then heated up to the maximum temperature.
If the "Defrost" function is active, the settings for air distribution, recirculated air and "A/C" are locked.
With code (582) Rear air conditioning, the symbols "OFF" and "Rear remote control" appear in the display of the rear air conditioning control unit. The rear air conditioner is switched off. The buttons of the rear air conditioning control unit are locked.
Additional function requirements for maximum cooling output (with code (494) USA version)
^ Maximum cooling output set by:
- Left temperature selection button (N72/1s34) or right temperature selection button (N72/1s41) in upper control panel control unit or
- Front central operating unit
Function sequence, maximum cooling output
Setting the maximum cooling output at the upper control panel control unit or at the front central operating unit raises the basic ventilation level to 100 %.
In COMAND display (A40/8) (without code (867) SPLITVIEW) or in SPLITVIEW display (A40/10) (with code (867) SPLITVIEW) the words "MAX COOL" are shown
With code (582) Rear air conditioning and "MONO" mode active, the rear air conditioning control unit receives the message "MAX COOL" from the AAC [KLA] control unit. This setting data is taken over by the rear air conditioning control unit. The words "MAX COOL" also appear in the rear display.
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 at the evaporator and at the rear air conditioning evaporator (with code (582) Rear air conditioning)
^ Function sequence, determining temperature downstream of the rear air conditioning heater heat exchanger (with code (582) Rear air conditioning)
^ Function sequence, determining the settings at the air outlets
^ Function sequence, determining the refrigerant pressure
^ Function sequence, determining the engine speed
^ Function sequence, determining the pollutant concentration of the outside air
^ Function sequence, determining the dew point temperature
^ Function sequence, determining the door status
^ Function sequence, determining the window position
^ Function sequence for determining the SHD position (with code (414) Power glass tilting/sliding roof) or the panoramic sliding sunroof position (with code (413) Panoramic glass sunroof with top sliding sunroof)
^ Function sequence for determination of VCS status
^ Function sequence, determining the settings at the upper control panel control unit and at the front central operating unit
^ Function sequence for determining the settings at the rear air conditioning control unit (with code (582) Rear air conditioning)
Function sequence, determining the outside temperature
The outside temperature is recorded by the outside temperature indicator temperature sensor (B14). The front SAM control unit with fuse and relay module (N10/1) reads in the value of the outside temperature directly and transmits it via the interior CAN to the AAC [KLA] control unit.
Function sequence, determining the interior temperature
The interior temperature is measured by the in-car temperature sensor (B10/4). The AAC [KLA] control unit reads in the value of the interior temperature directly, evaluates it and regulates the interior temperature largely independently of the flow conditions in the vehicle interior.
Function sequence, determining the coolant temperature
The value of the coolant temperature is used to control the blend air flaps, to actuate the heater circulation pump and for other internal computations.
The temperature of the engine coolant is measured by the coolant temperature sensor (B11/4). The ME-SFI [ME] control unit reads in the detected value of the coolant temperature sensor directly and provides it on the chassis CAN. The central gateway control unit forwards this via the interior CAN to the AAC [KLA] control unit.
Function sequence, determining the temperature at the air outlets in the vehicle
The temperature at the air outlets is measured by the left side air vent temperature sensor (B10/31), by the right side air vent temperature sensor (B10/32), by the left footwell temperature sensor (B10/35) and by the right footwell temperature sensor (B10/36).
The AAC [KLA] control unit reads in the values of the temperature sensors directly and regulates the outlet air temperatures of the particular air outlets.
Function sequence, determining the vehicle speed
The current vehicle speed is provided by the instrument cluster (A1) via the central CAN (CAN F). The central gateway control unit transmits this over the interior CAN to the AAC [KLA] control unit. 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 intensity and the angle of incidence of the solar radiation on the vehicle are recorded by the AAC [KLA] sun sensor (4 in total) (B32/2). The AAC [KLA] control unit reads in the data from the AAC [KLA] sun sensor (4 in total) via the A/C bus and adapts the interior temperature and the blower speed accordingly.
In the event of one-sided solar radiation, an adequate temperature difference is set between the left and the right regulated specified temperatures.
The AAC [KLA] sun sensor (4 in total) is connected to the front SAM control unit. The data is only looped through, however, and read in by the AAC [KLA] control unit.
Function sequence, determining the temperature at the evaporator and at the rear air conditioning evaporator (with code (582) Rear air conditioning)
To prevent the evaporator from icing up, the local temperature is constantly recorded. The temperature at the evaporator is recorded by the evaporator temperature sensor (B10/6). The temperature at the rear air conditioning evaporator is recorded by the rear air conditioning evaporator temperature sensor (B10/11) (with code (582) Rear air conditioning). The values for the evaporator temperature sensor are read in directly by the AAC [KLA] control unit.
If the evaporator temperature sinks to approx. T = 2 °C, the electric refrigerant compressor or the rear air conditioning refrigerant shutoff valve (Y67) (with code (582) Rear air conditioning) is switched off.
Function sequence, determining temperature downstream of the rear air conditioning heater heat exchanger (with code (582) Rear air conditioning)
The temperature of the air flow downstream of the rear air conditioning heater heat exchanger is measured by the left rear air conditioning heat exchanger temperature sensor (B10/9) and by the right rear air conditioning heat exchanger temperature sensor (B10/10).
The AAC [KLA] control unit reads in the values of the rear air conditioning heat exchanger temperature sensor directly, calculates the opening period of the left duovalve (A31/1y1) and the right duovalve (A31/1y2) in the rear heating system feed unit (A31/1), which are then actuated accordingly.
Function sequence, determining the settings at the air outlets
The settings at the air outlets are recorded by the following components:
- Left side air outlet potentiometer (R41/1)
- Right side air outlet potentiometer (R41/2)
- Left front center air outlet potentiometer (R41/3r1)
- Right front center air outlet potentiometer (R41/3r2)
- Left rear center air vent potentiometer (R41/4r1)
(with code (582) Rear air conditioning)
- Right rear center air vent potentiometer (R41/4r2)
(with code (582) Rear air conditioning)
The recorded values of the potentiometers are read in directly by the AAC [KLA] control unit.
Function sequence, determining the refrigerant pressure
The refrigerant pressure is registered by the refrigerant pressure sensor (B12). If the pressure is too high or too low, the AAC [KLA] control unit shuts off the electric refrigerant compressor.
The refrigerant pressure sensor is read in by the front SAM control unit and forwarded via interior CAN to the AAC [KLA] control unit.
Function sequence, determining the engine speed
The engine speed is used, among other things, to regulate the electric refrigerant compressor and is provided by the ME-SFI [ME] control unit via chassis CAN and forwarded by the central gateway control unit via interior CAN to the AAC [KLA] control unit.
Function sequence, determining the pollutant concentration of the outside air
The KLA [AAC] multifunction sensor (B31/1) records the pollutant concentration of harmful gases carbon monoxide (CO) and nitrogen oxide (NO X) in the outside air.
The values of the AAC [KLA] multifunction sensor are read in by the AAC [KLA] control unit via the A/C bus. The AAC [KLA] control unit controls the automatic recirculation according to the values read in.
The AAC [KLA] multifunction sensor is connected to the front SAM control unit. The data is only looped through, however, and read in by the AAC [KLA] control unit.
Function sequence, determining the dew point temperature
The AAC [KLA] multifunction sensor uses the ambient temperature and air humidity to calculate the dew point and makes this available to the AAC [KLA] control unit via the A/C bus. On reaching the dew point, the windows and the glass of the outside mirror begin to get fogged. To prevent this, the AAC [KLA] control unit activates the automatic air conditioning and the outside mirror heater.
In addition, the evaporator temperature and the opening angle of the defroster flaps are regulated depending on the dew point temperature.
Function sequence, determining the door status
When a vehicle door is open, the AAC [KLA] control unit calculates the current inside temperature after a short delay in order to prevent unnecessary readjustment in the event of large temperature differences between the inside and outside air.
The status of the particular vehicle doors is made available via interior CAN by the AAC [KLA] control unit:
- Left front door is recorded by left front rotary tumbler switch (A85s1) and provided by left front door control unit (N69/1)
- Right front door is recorded by right front rotary tumbler switch (A85/1s1) and provided by right front door control unit (N69/2
- Left rear door is recorded by left rear rotary tumbler switch (A85/3s1) and provided by left rear door control unit (N69/3)
- Right rear door is recorded by right rear rotary tumbler switch (A85/4s1) and provided by right rear door control unit (N69/4)
Function sequence, determining the window position
When the side windows are open, the AAC [KLA] control unit calculates the current inside temperature after a short delay in order to prevent unnecessary readjustment in the event of large temperature differences between the inside and outside air.
The positions of the side windows are made available to the AAC KLA] control unit via interior CAN:
- Left front side window by left front door control unit
- Right front side window by right front door control unit
- Left rear side window by left rear door control unit
- Right rear side window by right rear door control unit
Function sequence for determining the SHD position (with code (414) Power glass tilting/sliding roof) or the panoramic sliding sunroof position (with code (413) Panoramic glass sunroof with top sliding sunroof)
When the tilting/sliding roof or the panoramic sliding sunroof is open, the AAC [KLA] control unit calculates the current inside temperature after a short delay in order to prevent unnecessary readjustment in the event of large temperature differences between the inside and outside air.
The position of the tilting/sliding roof is made available via interior CAN by the overhead control panel control unit (N70) and read in by the AAC [KLA] control unit.
The position of the panoramic sliding sunroof is made available on the interior CAN by the panoramic sliding sunroof control module (A98) and read in by the AAC [KLA] control unit.
Function sequence for determination of VCS status
With active voice control system, the blower output of the blower regulator is limited. The COMAND controller unit (A40/3) sends the status of the voice control system via central CAN to the central gateway control unit and from there via interior CAN to the AAC [KLA] control unit.
Function sequence, determining the settings at the upper control panel control unit and at the front central operating unit
The automatic air conditioning functions can be set by the driver and the front passenger via the upper control panel control unit and the front central operating unit.
The settings at the upper control panel control unit are transmitted to the AAC [KLA] control unit via interior CAN.
The settings at the front central operating unit are forwarded to the COMAND controller unit via telematics CAN (CAN A), transferred via central CAN to the central gateway control unit and from there via the interior CAN to the AAC [KLA] control unit.
Function sequence for determining the settings at the rear air conditioning control unit (with code (582) Rear air conditioning)
The rear area automatic air conditioning functions can be adjusted by the rear occupants via the rear air conditioning control unit. The rear AC control unit is a pure operating unit. The settings at the rear air conditioning control unit are forwarded to the COMAND controller unit via the telematics CAN, transferred via the central CAN to the central gateway control unit and from there via the interior CAN to the AAC [KLA] control unit. The AAC [KLA] control unit performs all the actuations of the automatic air conditioning functions in the rear.
AC component actuation function sequence
The AC component actuation function sequence comprises the following subfunctions:
^ Function sequence for actuation of the electric refrigerant compressor
^ Function sequence for actuation of blower motor and rear blower motor (M2/1) (with code (582) Rear air conditioning)
^ 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 for actuation of the electric refrigerant compressor
The electric refrigerant compressor control unit is responsible for the intake and compression of the refrigerant. The electric refrigerant compressor is controlled with regard to rpm continuously from U = 700 to 9000 rpm by the AAC [KLA] control unit. The AAC [KLA] control unit sends the request to switch on via interior CAN to the central gateway control unit.
This routes the request via chassis CAN to ME-SFI [ME] control unit. The ME-SFI [ME] control unit then actuates the electric refrigerant compressor via drive train sensor CAN (CAN I).This routes the request via chassis CAN to ME-SFI [ME] control unit. The ME-SFI [ME] control unit then actuates the electric refrigerant compressor via drive train sensor CAN (CAN I).
Function sequence for actuation of blower motor and rear blower motor (M2/1) (with code (582) Rear air conditioning)
In accordance with the position of the fresh air/air recirculation flap, the interior air is circulated or fresh air is supplied by actuating the blower motor and the rear blower motor.
The blower motor is actuated by means of the blower regulator and the rear blower motor is actuated by means of the rear air conditioning electronic blower regulator (N29/2) (with code (582) Rear air conditioning), in each case with the power regulated within a range of P = 0 to 100 %.
The blower regulator is actuated via the climate control LIN and the rear air conditioning electronic blower regulator is actuated directly by the AAC [KLA] control unit.
Depending on the control voltage, the blower regulators control the operating voltage for the blower motor from U = 0 to 12.5 V and for the rear blower motor from U = 0 to 12 V, and thus the rpm of each blower motor from 0 to 100 %.
With VCS [SBS] active, the blower output is limited.
Air ducting flaps actuation function sequence
The air distribution in the vehicle interior is controlled by the corresponding adjustment of the air ducting flaps in the air conditioner housing.
The following components are actuated by the AAC [KLA] control unit via the climate control LIN:
- for fresh air/recirculated air control:
- Fresh air/air recirculation flap actuator motor (M2/5)
- for temperature control:
- Upper left blend air flap actuator motor (M2/30)
- Lower left blend air flap actuator motor (M2/31
- Upper right blend air flap actuator motor (M2/32)
- Lower right blend air flap actuator motor (M2/33)
- for ventilation control:
- Left defroster flap actuator motor (M2/8)
- Right defroster flap actuator motor (M2/9)
- Left footwell flap actuator motor (M2/10)
- Right footwell flap actuator motor (M2/11)
- Left center air flap actuator motor (M2/12)
- Right center air flap actuator motor (M2/13)
- Left side air vent flap actuator motor (M2/17)
- Right side air vent flap actuator motor (M2/18)
- Left rear center air vent actuator motor (M16/19)
(with code (582) Rear air conditioning)
- Right rear center air vent actuator motor (M16/20)
(with code (582) Rear air conditioning)
- Left B-pillar air distribution actuator motor (M16/33)
- Right B-pillar air distribution actuator motor (M16/34)
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 AAC [KLA] control unit calculates the target fan speed of the electric suction fan depending on the refrigerant pressure and transmits the request to the central gateway control unit via the interior CAN.
The central gateway control unit forwards the request via chassis CAN to the ME-SFI [ME] control unit. The ME-SFI [ME] control unit then calculates the target rpm depending on the engine temperature and compares it with the automatic air conditioning request. Then the electric radiator fan is actuated correspondingly by the ME-SFI [ME] control unit.
