GF83.40-P-2004LE Regulation of Automatic Air Conditioning, Function
GF83.40-P-2004LE 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).
The circuit status of circuit 61 is made available on the chassis CAN (CAN E) by the CDI control unit (N3/9) (for diesel engine) or by the ME-SFI [ME] control unit (N3/10) (for gasoline engine) and forwarded from the central gateway control unit (N93) via the interior CAN to the AAC [KLA] control unit (N22/1).
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 will be described following the description of the settings 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 (ACB) and direct lines.
This in turn makes it possible to incorporate relevant parameters in order to improve the regulation quality of the automatic air conditioning and to lower power consumption.
The automatic air conditioning regulation 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) on the upper control panel control unit (LED lights up)
- Front central operating unit or
- Function mode button on 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 (SR) position (model 216.3, model 221.1 or model 221.0 with code (414) Power glass tilting/sliding roof) or panoramic sliding sunroof position (model 221.1 with code (413) Panoramic glass sunroof with top sliding sunroof) Status of voice control system (VCS)
- Status of voice control system (VCS)
- Settings at the upper control panel control unit, at the front central operating unit or at the rear air conditioning control unit
Additional function requirements, manual regulation
^ Air distribution manually changed by:
- Front central operating unit or
- Air distribution buttons on the rear air conditioning control unit
^ Air volume manually changed by:
- Left blower button (N72/1s35) or
right blower button (N72/1s40) on the upper control panel control unit or
- Front central operating unit or
- Air volume buttons on the 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
^ Defrost function activated with defrost/heated windshield button (N72/1s36) on the upper control panel control unit (LED lights up)
Function sequence of defroster function
Pressing the defrost/heated windshield button on the upper control panel control unit closes all the air flaps except for the defroster flaps and the fresh air flap, which are opened completely.
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 engine coolant is cold, the air volume is reduced.
The air conditioner water valve (Y19/2) is opened, and the heater circulation pump (M13) and if necessary the PTC heater booster (R22/3) (with diesel engine) are 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 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.
If the "Defrost" function is active, the settings for air distribution, recirculated air and AC are locked.
With code (582) Rear air conditioner, 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 prerequisite, 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) on the upper control panel control unit or
- Front central operating unit
Function sequence, maximum cooling output (with code (494) USA version)
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%.
The words "MAX COOL" appear on the COMAND display (A40/8) (without code (867) SPLITVIEW) or on the SPLITVIEW display (A40/10) (with code (867) SPLITVIEW).
With code (582) Air conditioning in rear and active "MONO" mode, the rear air conditioning control unit receives the message "MAX COOL" from the AAC control unit. This setting data is taken over by the rear air conditioning control unit. The words "MAX COOL" also appear on 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, determining tilting/sliding roof position (model 216.3, model 221.1 or model 221.0 with code (414) Power glass tilting/sliding roof) or the panoramic sliding sunroof position (model 221.1 with code (413) Panoramic glass sunroof with top sliding sunroof)
^ Function sequence, determining VCS status
^ Function sequence, determining the settings at the upper control panel control unit and at the front central operating unit
^ Function sequence, 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 over 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 many other internal computations.
The temperature of the engine coolant is measured by the coolant temperature sensor (B11/4). The CDI control unit or ME control unit reads in the valued measured by the coolant temperature sensor directly and provides it on the vehicle CAN. The central gateway control unit relay this value to the AAC control unit via the interior CAN.
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 made available on the central CAN (CAN F) by the instrument cluster (A1). 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.
Function sequence, determining the temperature at the evaporator and at the rear air conditioning evaporator (with code (582) Rear air conditioning)
The local temperature is measured permanently to prevent the evaporator from icing up. The evaporator temperature is recorded by the evaporator temperature sensor (B10/6). The temperature at the rear air conditioning evaporator is measured 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 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 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)
(model 221 with code (582) Rear air conditioning)
- Right rear center air vent potentiometer (R41/4r2)
(model 221 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). The refrigerant pressure sensor is read in directly by the AAC [KLA] control unit.
If the pressure is too high or too low, the AAC [KLA] control unit shuts off the refrigerant compressor.
Function sequence, determining the engine speed
The engine speed is used, among other things, to regulate the refrigerant compressor and is made available on the chassis CAN by the CDI control unit or by the ME-SFI [ME] control unit and forwarded from the central gateway control unit via the interior CAN to the AAC [KLA] control unit.
Function sequence, determining the pollutant concentration of the outside air
The comfort automatic air conditioning multifunction sensor (B31/1) records the pollutant concentration of the carbon monoxide (CO) and nitrogen oxide (NO X) pollutants 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.
Function sequence, determining the dew point temperature
The multifunction sensor AAC 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.
Moreover, the evaporator temperature and opening angle of the defroster flaps are controlled, depending on the dewpoint 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 on the interior CAN by the AAC [KLA] control unit:
- Left front door is recorded by the left rotary tumbler switch (A85s1) (model 216) or by the left front rotary tumbler switch (A85s1) (model 221) and made available by the left door control unit (N69/1) (model 216) or by the left front door control unit (N69/1) (model 221)
- Right front door is recorded by the right rotary tumbler switch (A85/1s1) (model 216) or by the right front rotary tumbler switch (A85/1s1) (model 221) and made available by the right door control unit (N69/2) (model 216) or by the right front door control unit (N69/2) (model 221)
- Left rear door (model 221) is recorded by the left rear rotary tumbler switch (A85/3s1) and made available by the left rear door control unit (N69/3)
- Right rear door (model 221) is recorded by the right rear rotary tumbler switch (A85/4s1) and made available by the 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 on the interior CAN by the AAC [KLA] control unit:
- Left front side window by the left door control unit (model 216) or by the left front door control unit (model 221)
- Right front side window by the right door control unit (model 216) or by the right front door control unit (model 221)
- Rear side windows (model 216) by the rear control unit (N22/6)
- Left rear side window (model 221) by the left rear door control unit
- Right rear side window (model 221) by the right rear door control unit
Function sequence, determining the SR position or the panoramic sliding sunroof position (model 216.3, model 221.1 or model 221.0 with code (414) Power glass tilting/sliding roof) or the panoramic sliding sunroof position (model 221.1 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 on the 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, determining VCS status
When the VCS is active, the blower output is limited by the blower regulator. The COMAND control unit (A40/3) sends the status of the VCS via the central CAN to the central gateway control unit and from there, via the interior CAN to the AAC 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 the interior CAN.
The settings at the front central operating unit are forwarded to the COMAND controller unit via the telematics CAN (CAN A), transferred via the central CAN to the central gateway control unit and from there via the interior CAN to the AAC [KLA] control unit.
Function sequence, 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, actuation of the refrigerant compressor
^ Function sequence, actuation of the blower motor and the rear blower motor (M2/1) (with code (582) Rear air conditioning)
^ Function sequence, actuation of the PTC heater booster (for diesel engine)
^ 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 P = 100% by the AAC [KLA] control unit via the compressor control valve.
The AAC [KLA] control unit transmits the refrigerant compressor switch-on request directly to the compressor control valve.
Function sequence, actuation of the blower motor and the rear blower motor (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, 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 control unit. Depending on the control voltage, the blower regulators regulate 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 rotational speed of the particular blower motor from 0 up to 100 %.
When the VCS is active, the blower output is limited.
Function sequence, actuation of the PTC heater booster
(for diesel engine)
On vehicles with diesel engine, the PTC heater booster is activated via the climate control LIN if required.
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)
(model 221 with code (582) Rear air conditioning)
- Right rear center air vent actuator motor (M16/20)
(model 221 with code (582) Rear air conditioning)
- Left B-pillar air distribution actuator motor (M16/33)
(model 221)
- Right B-pillar air distribution actuator motor (M16/34)
(model 221))
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 to the CDI control unit or to the ME-SFI [ME] control unit via 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 it with the automatic air conditioning request.
The electric suction fan is then actuated accordingly by the CDI control unit or by the ME-SFI [ME] control unit.
