Regulation of Automatic air conditioning, function

P83.40-4887-79

P83.40-4888-79

Function requirements, general

 Terminal 15 ON

 Automatic air conditioning switched on

For cooling operation:

 Engine running (except model 212.095/098/298)

 Refrigerant compressor switched on (model 212 (except model 212.095/098/298) except CODE B09 (Refrigerant compressor with magnetic clutch))

 Electric refrigerant compressor switched on (model 212.095/098/298)

 Refrigerant compressor with magnetic clutch switched on (with CODE B09 (Refrigerant compressor with magnetic clutch))

 The electronic ignition lock control unit transmits the status of circuit 15 via the interior CAN to the automatic air conditioning control and operating unit. The CDI control unit (with diesel engine) or the ME-SFI [ME] control unit (with gasoline engine) sends the "Engine running" signal on vehicles up to 28.02.2013 over the chassis CAN, front SAM control unit and interior CAN to the automatic air conditioning control and operating unit. On vehicles as of 01.03.2013, the CDI control unit (with diesel engine) or the ME-SFI [ME] control unit (with gasoline engine) sends this signal over the chassis CAN 1, front SAM control unit and interior CAN to the automatic air conditioning control and operating unit.

Automatic air conditioning regulation, general

The electronic temperature control and the air distribution in the vehicle interior take place depending on the settings made at the automatic air conditioning control and operating unit, the rear automatic air conditioning operating unit (with CODE (581) Comfort automatic air conditioning) and on the variables recorded by different sensors (e.g. interior temperature, outside temperature, coolant temperature, vehicle speed). Determination of these variables is described below.

The automatic air conditioning control and operating unit is networked via the interior CAN and climate control LIN with the vehicle electronics system. This in turn makes it possible to incorporate relevant parameters in order to improve regulation quality and to lower power consumption.

 If settings are altered on the automatic air conditioning control and operating unit that affect the temperature, the air distribution or the air flow, then the relevant adjustment values are shown briefly in the Audio/COMAND display (A40/8).

The automatic air conditioning control function encompasses the following subfunctions:

 Function sequence for recording and evaluating variables

 Function sequence for AC component actuation

 Fresh air mode function sequence

 Air recirculation mode function sequence

 Function sequence for defroster function

 Function sequence for evaporator drying process

 Function sequence for residual heat utilization (with CODE 581 (Comfort automatic air conditioning) or with CODE 965 (Electrical preinstallation for rental car))

 Function sequence for air conditioning shutoff in the event of a crash (as of 01.03.2013)

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

 Function sequence for ram air operation

Function sequence for recording and evaluating variables

The following variables are recorded and evaluated:

 Outside temperature

 Interior temperature

 Temperature at the air outlets in the vehicle

 Temperature and humidity of the windshield (as of 01.12.2009 or with CODE B03 (ECO start/stop function))

 Dew point temperature (up to 31.05.2010 with CODE 581 (Comfort automatic air conditioning))

 Coolant temperature

 Temperature on evaporator

 Refrigerant pressure

 Solar radiation

 Outside air pollutant concentration (with CODE 581 (Comfort automatic air conditioning))

 Vehicle speed

 Engine rpm (except model 212.095/098/298)

 Door status

 Side window position

 Position of sliding roof (SD) (with CODE 414 (Power glass tilting/sliding roof)) or panoramic sliding sunroof (with CODE 413 (Panoramic glass sunroof with top sliding sunroof))

 Settings on rear automatic air conditioning operating unit (with CODE 581 (Comfort automatic air conditioning))

 Status of voice control system (VCS) (with CODE 511 (Audio 50 APS with DVD changer) or CODE 512 (COMAND APS with DVD changer) or CODE 527 (COMAND APS with single DVD drive (with navigation)) or CODE 531 (COMAND APS))

Outside temperature

The outside temperature sensor measures the outside temperature. The front SAM control unit reads in the signal of the outside temperature sensor directly, calculates the outside temperature and transmits this via the interior CAN to the automatic air conditioning control and operating unit. The automatic air conditioning control and operating unit requires 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.

Interior temperature

Roof area:

With CODE 414 (Power glass tilting/sliding roof), the interior temperature in the roof area is recorded by the interior temperature sensor with integrated fan in the overhead control panel control unit. The overhead control panel control unit calculates the interior temperature and sends it via interior CAN to the automatic air conditioning control and operating unit. Except CODE 414 (Power glass tilting/sliding roof), the interior temperature in the roof area is recorded by the interior temperature sensor with integrated fan in the electronic overhead control panel. The signals of the interior temperature sensor with integrated fan are read in directly by the automatic air conditioning control and operating unit. The interior temperature sensors are each equipped with a fan that draws the air in from the vehicle interior for the temperature measurement.

Instrument panel:

The interior temperature in the area of the instrument panel is measured by the interior temperature sensor. The signals of the interior temperature sensor are read in directly by the automatic air conditioning control and operating unit.

 Because the interior air is constantly circulated by the fan, a precise temperature measurement is ensured. This enables a temperature control to be achieved that is mainly independent of the airflow conditions in the vehicle interior.

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 in the following situations by the automatic air conditioning control and operating unit:

 Side window open

 Door open

This ensures that the air conditioning system immediately continues operation at the set specified temperature.

Temperature at the air outlets in the vehicle

The temperature at the air outlets in the vehicle are recorded by the air outlet temperature sensor. The automatic air conditioning control and operating unit regulates the air outlet temperature at the respective air outlets.

The signals of the air outlet temperature sensors are read in directly by the automatic air conditioning control and operating unit.

 MODEL 212 up to 2/28/11
with CODE 581 (Automatic air conditioning)
The rear footwell vent air outlet temperature sensor is also installed at the air outlet in the rear.

Temperature and humidity of windshield (as of 01.12.2009 or with CODE B03 (ECO start/stop function))

The vehicle interior humidity/temperature sensor measures the relative air humidity and the temperature directly on the inside of the windshield and determines the dew point temperature. The signals of the vehicle interior humidity/temperature sensor are read in by the automatic air conditioning control and operating unit via the climate control LIN. If there is a risk of the windows fogging up, appropriate countermeasures are taken such as switching on the refrigerant compressor or starting the engine (with CODE B03 (ECO start/stop function)).

Dew point temperature (up to 31.05.2010 with CODE 581 (Comfort automatic air conditioning))

The dew point is determined from the ambient temperature and the air humidity. The automatic air conditioning control and operating unit reads in the signals of the dew point sensor via the climate control LIN and calculates the dew point. When the dew point is reached, the windows and the outside mirrors start to fog up. To prevent this, the air conditioning system and the outside mirror heater are activated.

Coolant temperature

The temperature of the coolant is recorded by the coolant temperature sensor. The CDI control unit or the ME-SFI [ME] control unit reads in the resistance value directly, uses it to calculate the coolant temperature and, for vehicles up to 28.02.2013, sends this over the chassis CAN, front SAM control unit and interior CAN to the automatic air conditioning control and operating unit. In vehicles as of 01.03.2013 the CDI control unit or the ME-SFI [ME] control unit transmits this signal via the chassis CAN, the front SAM control unit and the interior CAN to the automatic air conditioning control and operating unit. The value is used to control the blend air flaps, regulate the PTC heater booster (engine 271.8, 274.9, 642.8 up to 28.02.2013 or 651.9) and actuate the coolant circulation pump (with CODE 581 (Comfort automatic air conditioning) or CODE 965 (Electrical preinstallation for rental vehicle) or CODE B03 (ECO start/stop function) or model 212.095/098/298).

Temperature on evaporator

To prevent the evaporator from icing up, the temperature there is recorded by the evaporator temperature sensor. The automatic air conditioning control and operating unit reads in the evaporator temperature sensor signal directly. If the evaporator temperature drops to approx. T  2 °C, the refrigerant compressor is switched off.

Refrigerant pressure

The refrigerant pressure is recorded by the refrigerant pressure sensor. The front SAM control unit reads in the signal of the refrigerant pressure sensor directly. The front SAM control unit transmits the value of the refrigerant pressure via the interior CAN to the automatic air conditioning control and operating unit. The pressure is compared with a stored temperature/pressure curve. At a refrigerant pressure p < 1.7 or p > 30 bar, the refrigerant compressor is switched off or not switched in.

Solar radiation

The sun sensor records the angle of incidence and the intensity of the solar radiation on the vehicle. The automatic air conditioning control and operating unit reads in the signals of the sun sensor directly. The interior temperature and blower speed are adjusted according to the values. In the event of one-sided solar radiation, an appropriate temperature difference is set between the left and the right specified control temperatures.

Outside air pollutant concentration (with CODE 581 (Comfort automatic air conditioning))

The pollutant sensor records the following environmental influences:

 Carbon monoxide level (CO)

 Nitrogen oxide (NOx)

 Outside dew point temperature

 Relative air humidity

 Outside temperature

The automatic air conditioning control and operating unit reads in the signals of the pollutant sensor via the climate control LIN. The automatic air conditioning control and operating unit controls the automatic recirculation depending on read in values.

Vehicle speed

The instrument cluster transmits the vehicle speed via the interior CAN to the automatic air conditioning control and operating unit. The vehicle speed is used to control the ram air function and for internal calculation of the outside temperature.

Engine rpm (except model 212.095/098/298)

The engine speed is recorded by the CDI control unit or by the ME-SFI [ME] control unit. The CDI control unit or the ME-SFI [ME] control unit sends the signal for vehicles up to 28.02.2013 over the chassis CAN, front SAM control unit and over the interior CAN to the automatic air conditioning control and operating unit. On vehicles as of 01.03.2013, the CDI control unit or the ME-SFI [ME] control unit sends the signal over chassis CAN 1, the front SAM control unit and over the interior CAN to the automatic air conditioning control and operating unit. The engine speed is used among others to regulate the refrigerant compressor.

Door status

The status of each door is determined by the following control units and transmitted via the interior CAN to the automatic air conditioning control and operating unit:

 Left front door control unit

 Right front door control unit

 Rear SAM control unit

If the door is open, the automatic air conditioning control and operating unit retains the current blower output in order to avoid unnecessary readjustment in the event of large differences between the air temperature inside and outside the vehicle.

Side window position

The position of the respective side window is determined by the following control units and transmitted via the interior CAN to the automatic air conditioning control and operating unit:

 Left front door control unit

 Right front door control unit

 Left rear door control unit

 Right rear door control unit

If the side window is open, the automatic air conditioning control and operating unit retains the current blower output in order to avoid unnecessary readjustment in the event of large differences between the air temperature inside and outside the vehicle.

Position of sliding roof (with CODE 414 (Power glass tilting/sliding roof)) or panoramic sliding sunroof (with CODE 413 (Panoramic glass sunroof with top sliding sunroof))

The position of the tilting/sliding roof is transmitted by the overhead control panel control unit via the interior CAN to the automatic air conditioning control and operating unit.

The position of the panoramic sliding sunroof is transmitted by the panoramic sliding sunroof control unit via the interior CAN to the automatic air conditioning control and operating unit.

If the sliding roof is open, the automatic air conditioning control and operating unit retains the current blower output in order to avoid unnecessary readjustment in the event of large differences between the air temperature inside and outside the vehicle.

Settings on rear automatic air conditioning operating unit (with CODE 581 (Comfort automatic air conditioning))

The climate control of the rear compartment can be adjusted by the rear passengers via the rear automatic air conditioning operating unit. Operation of the rockers for controlling the temperature and the blower setting on the rear automatic air conditioning operating unit is read in via the climate control LIN by the automatic air conditioning control and operating unit. This data is used to control the air flow of the rear vents via the rear blower motor and the temperature in the rear via the rear blend air flap actuator motor.

The rear blower motor and the rear blend air flap actuator motor are actuated by the automatic air conditioning control and operating unit via climate control LIN.

Status of VCS (with CODE 511 (Audio 50 APS with DVD changer) or CODE 512 (COMAND APS with DVD changer) or CODE 527 (COMAND APS with single DVD drive (with navigation)) or CODE 531 (COMAND APS))

With VCS [SBS] active, the blower output is limited. The radio with auto pilot system or the COMAND controller unit transmits the status of the VCS via the interior CAN to the automatic air conditioning control and operating unit.

Function sequence for AC component actuation

The function sequence for actuating the A/C components encompasses the following subfunctions:

 Function sequence for actuation of blower motor

 Function sequence for actuation of the air ducting flaps

 Function sequence for actuation of the refrigerant compressor (except model 212.095/098/298)

 Function sequence for actuation of electric refrigerant compressor (model 212.095/098/298)

 Function sequence for actuation of the fan motor

 Function sequence for actuation of PTC heater booster (engine 271.8, 274.9, 642.8 up to 28.02.2013 or engine 651.9)

 Function sequence for actuation of evaporator shutoff valve (model 212.095/098/298)

 Function sequence for actuation of coolant circulation pump (with CODE 581 (Comfort automatic air conditioning) or CODE 965 (Electrical preinstallation for rental vehicle) and CODE B03 (ECO start/stop function) or model 212.095/098/298)

 Function sequence for actuation of high-voltage battery cooling system shutoff valve (model 212.095/098/298)

Function sequence for actuation of blower motor

Ventilation is achieved with the aid of the blower motor. The automatic air conditioning 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 assisted by the rear blower motor.

The rear blower motor is actuated via the climate control LIN by the automatic air conditioning control and operating unit.

 MODEL 212 as of 3/1/13
The blower motor is switched off in the event of an accident.

 MODEL 212
with CODE 511 (Audio 50 APS with DVD changer)
MODEL 212
with CODE 512 (COMAND APS with DVD changer)
MODEL 212
with CODE 527 (COMAND APS with single DVD drive (with navigation))
MODEL 212
with CODE 531 (COMAND APS)
With VCS [SBS] active, the blower output is limited.

 MODEL 212
with CODE B03 (ECO start/stop function)
The blower output is limited by the automatic air conditioning control and operating unit when the engine is switched off. The CDI control unit or the ME-SFI [ME] control unit transmits the status "Engine running" in vehicles up to 28.02.2013 via the chassis CAN, the front SAM control unit and the interior CAN to the automatic air conditioning control and operating unit. In vehicles as of 01.03.2013 the CDI control unit or the ME-SFI [ME] control unit transmits the "Engine running" status via chassis CAN 1, the front SAM control unit and the interior CAN to the automatic air conditioning control and operating unit.

Function sequence for actuation of the air ducting flaps

The air distribution in the vehicle interior is controlled by adjusting the air ducting flaps in the air conditioner housing. The automatic air conditioning control and operating unit actuates the following components via climate control LIN:

Vehicles except CODE 581 (Comfort automatic air conditioning):

 Fresh air/recirculated air flap via the fresh air/recirculated air flap actuator motor (fresh air/recirculated air control and ram air control)

 Left blend air flap via left blend air flap actuator motor (temperature control)

 Right blend air flap via the right blend air flap actuator motor (temperature control)

 Defroster flap over the defroster flap actuator motor (ventilation control)

 Air distribution flap via the air distribution flap actuator motor (ventilation control)

Vehicles with CODE 581 (Comfort automatic air conditioning):

 Fresh air/recirculated air flap via the fresh air/recirculated air flap actuator motor (fresh air/recirculated air control)

 Left blend air flap via left blend air flap actuator motor (temperature control)

 Right blend air flap via the right blend air flap actuator motor (temperature control)

 Rear blend air flap over the rear blend air flap actuator motor (temperature control)

 Left defroster flap via left defroster flap actuator motor (ventilation control)

 Right defroster flap via right defroster flap actuator motor (ventilation control)

 Left footwell flap via left footwell flap actuator motor (ventilation control)

 Right footwell flap via right footwell flap actuator motor (ventilation control)

 Left center air vent flap via left center air vent flap actuator motor (ventilation control)

 Right center air vent flap via right center air vent flap actuator motor (ventilation control)

 Diffuser flap via the diffuser flap actuator motor (ventilation control)

 Left B-pillar air distribution via left B-pillar air distribution actuator motor (ventilation control)

 Right B-pillar air distribution via right B-pillar air distribution actuator motor (ventilation control)

 Ram air flap via the ram air flap actuator motor (up to 31.05.2010) (ram air control)

 Fresh air/recirculated air flap via the fresh air/recirculated air flap actuator motor (as of 01.06.2010) (ram air control)

 MODEL 212 as of 3/1/13
The fresh air/recirculated air flap is closed after an accident.

 In order to prevent fogging of windows, the defroster flaps are closed t = 2 min. after switching off circuit 15. After starting the engine, the defroster flaps remain in this position for approx. t = 30 s. After that, all adjustments are possible again.

 In the event of "Circuit 15 OFF", when one of the doors is opened the fresh air/recirculated air flap is set to partial air recirculation by the fresh air/recirculated air flap actuator motor, and the ram air flap (with CODE 581 (Comfort automatic air conditioning)) is set to partial air recirculation by the ram air flap actuator motor (up to 31.05.2010) or the fresh air/recirculated air flap actuator motor (as of 01.06.2010). This achieves a significant reduction in the door closing forces. The function can be set with the diagnostic tester.

P83.10-2677-78

P83.10-2678-72

P83.10-2679-81

Function sequence for actuation of the refrigerant compressor (except model 212.095/098/298)

The refrigerant compressor is responsible for induction and compression of the refrigerant. The refrigerant compressor output is regulated continuously up to 100 % by the AAC control and operating unit via the compressor control valve. The automatic air conditioning control and operating unit transmits the request via the interior CAN to the front SAM control unit. This receives the request and actuates the refrigerant compressor control valve.

With CODE B09 (Refrigerant compressor with magnetic clutch), a magnetic clutch is also installed. This can be used to completely disconnect the refrigerant compressor from the belt drive power flow. This in turn enables additional fuel savings to be made. The automatic air conditioning control and operating unit transmits the request via the interior CAN to the front SAM control unit. This directly actuates the refrigerant compressor magnetic clutch.

The automatic air conditioning control and operating unit also transmits the request for the idle speed increase via the interior CAN, the front SAM control unit and the chassis CAN (up to 28.02.2013) or chassis CAN 1 (as of 01.03.2013) to the ME-SFI [ME] control unit or the CDI control unit. This increases the idle speed in accordance with the additional load that occurs when the refrigerant compressor is switched on.

 MODEL 212 as of 3/1/13
In the event of an accident, the refrigerant compressor is shut off via the refrigerant compressor regulation valve or the refrigerant compressor magnetic clutch (with CODE B09 (Refrigerant compressor with magnetic clutch)).

Function sequence for actuation of the electric refrigerant compressor (model 212.095/098/298)

The electric refrigerant compressor is responsible for the intake and compression of the refrigerant. The speed of the electric refrigerant compressor is continuously regulated as a function of the evaporator temperature from n = 700 up to 9000 rpm. The automatic air conditioning control and operating unit transmits the request via the interior CAN, the front SAM control unit and the chassis CAN (up to 28.02.2013) or chassis CAN 1 (as of 01.03.2013) to the CDI control unit or the ME-SFI [ME] control unit. The CDI control unit or the ME-SFI [ME] control unit transmits the request via the hybrid CAN to the electric refrigerant compressor.

Function sequence for actuation of the fan motor

The fan motor is used for cooling the coolant and refrigerant. The automatic air conditioning control and operating unit calculates the specified fan speed depending on the refrigerant pressure and transmits the request via the interior CAN, the front SAM control unit and the chassis CAN (up to 28.02.2013) or chassis CAN 1 (as of 01.03.2013) to the CDI control unit or the ME-SFI [ME] control unit. The CDI control unit or ME-SFI [ME] control unit calculates the specified fan speed depending on the engine temperature, compares this with the request from the automatic air conditioning control and operating unit and actuates the fan motor accordingly.

Function sequence for actuation of the PTC heater booster (engine 271.8, 274.9, 642.8 up to 28.02.2013 or engine 651.9)

The PTC heater booster makes it possible to heat up the vehicle interior quickly. The PTC heater booster is switched on and off by the automatic air conditioning control and operating unit via the climate control LIN.

 MODEL 212 as of 3/1/13
The PTC heater booster is switched off in the event of an accident.

Function sequence for actuation of the evaporator shutoff valve (model 212.095/098/298)

The evaporator shutoff valve is used to control the flow of refrigerant to the evaporator. Actuation takes places depending on the settings on the automatic air conditioning control and operating unit. The automatic air conditioning control and operating unit transmits the request for the actuation of the evaporator shutoff valve via the interior CAN to the front SAM control unit. This actuates the evaporator shutoff valve.

Function sequence for actuation of the coolant circulation pump (with CODE 581 (Comfort automatic air conditioning) or CODE 965 (Electrical preinstallation for rental vehicle) or CODE B03 (ECO start/stop function) or model 212.095/098/298)

The coolant circulation pump is used to pump coolant through the heater heat exchanger when the engine is running or when residual heat mode is enabled (except CODE 494 (USA version)).

The automatic air conditioning control and operating unit transmits the request for actuation of the coolant circulation pump via the interior CAN to the front SAM control unit. This controls the coolant circulation pump accordingly.

Function sequence for actuation of high-voltage battery cooling system shutoff valve (model 212.095/098/298)

The high voltage battery cooling system shutoff valve is used to control the flow of coolant into the evaporator that is integrated in the high-voltage power supply. This removes thermal energy from the high-voltage power supply and prevents any overheating. The request for actuating the high-voltage battery cooling system shutoff valve is transmitted by the CDI control unit or the ME-SFI [ME] control unit via hybrid CAN to the battery management system control unit, which actuates the high-voltage battery cooling system shutoff valve directly.

Fresh air mode function sequence

In fresh air mode, the fresh air/recirculated air flap is opened and fresh air is delivered into the vehicle interior through the air conditioner housing.

Air recirculation mode function sequence

The air recirculation mode function sequence provides the following operating modes:

 Air recirculation mode via the air recirculation mode button

 Pollutant-controlled air recirculation mode (with CODE 581 (Comfort automatic air conditioning))

Air recirculation mode via the air recirculation mode button

When the air recirculation mode button on the automatic air conditioning control and operating unit is pressed for t < 1.5 s, the fresh air/recirculated air flap is closed to prevent air entering from outside. The air only circulates in the vehicle interior and unpleasant odors and harmful gases are kept out. The LED above the air recirculation mode button lights up during air recirculation mode.

The automatic air conditioning control and operating unit reads in the status of the air recirculation mode button directly and actuates the fresh air/recirculated air flap actuator motor via climate control LIN.

If the air recirculation mode button is pressed for t > 1.5 s, the side windows, the panoramic sliding sunroof (with CODE 413 (Panoramic glass sunroof with top sliding sunroof)) or the sliding roof (with CODE 414 (Power glass tilting/sliding roof)) are closed. If the air recirculation mode button is then pressed for t > 1.5 s, the side windows and the sliding roof are moved back to the default position (provided that they were not manually adjusted during air recirculation mode).

 Detailed information on this is available in the function description "Theft protection and locking function description" in the subfunction "Convenience feature (CF [KFB]), function".

 MODEL 212
with CODE 460 (Canada version)
MODEL 212
with CODE 494 (US version)
Comfort air recirculation closing is not possible.

Additional function requirements for pollutant- controlled air recirculation mode

 Refrigerant compressor switched on (model 212 (except model 212.095/098/298) except CODE B09 (Refrigerant compressor with magnetic clutch)) or

 Electric refrigerant compressor switched on (model 212.095/098/298) or

 Refrigerant compressor with magnetic clutch switched on (with CODE B09 (Refrigerant compressor with magnetic clutch))

Pollutant-controlled air recirculation mode (with CODE 581 (Comfort automatic air conditioning))

The pollutant sensor records the pollutant levels of the outside air. The automatic air conditioning control and operating unit reads in the signals of the pollutant sensor via the climate control LIN. Starting from a certain pollutant concentration, the fresh air/recirculated air flap is automatically set to the recirculated air position. Outside air supply is prevented and only the inside air is recirculated. If the conditions for the pollutant-controlled air recirculation mode exist after the engine is started, a supply of fresh air is first provided for t = 30 s. Operation initially continues with 80 % pollutant-controlled recirculated air and then with 100 % pollutant-controlled recirculated air after another t = 10 s.

 Pollutant-controlled air recirculation mode is not indicated via the LED in the air recirculation mode button.

Function sequence for defroster function

By pressing the defrosting button on the automatic air conditioning control and operating unit, all air flaps are closed, except 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 is actuated by the automatic air conditioning control and operating unit via the blower regulator in such a way that efficient defrosting is provided, depending on the temperature of the air flowing out.

The refrigerant compressor or the electric refrigerant compressor is switched on. The air is dried and then heated up to the maximum temperature.

 With CODE 581 (Comfort automatic air conditioning), defrost mode is operated separately for the driver via the left defroster flap actuator motor and for the front passenger via the right defroster flap actuator motor. Except CODE 581 (Comfort automatic air conditioning), defrosting is carried out for both the driver and the front passenger via the defroster flap actuator motor.

Additional function requirements for evaporator drying process

 Air conditioning was active at least once during the last ignition cycle

 Evaporator temperature T > 3 °C

 Engine Off

 Doors closed

 Kilometer reading > 250 km

Function sequence for evaporator drying process

To counteract evaporator odors in the vehicle interior and fogging of windows when starting the air conditioning, an evaporator drying process is performed.

With "engine OFF", a timer is activated in the instrument cluster. In vehicles up to 28.02.2013 the CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" signal over the chassis CAN to the instrument cluster. In vehicles as of 01.03.2013 the CDI control unit or the ME-SFI [ME] control unit sends the signal over the chassis CAN 1, front SAM control unit and the chassis CAN 2 to the instrument cluster.

After a waiting time of t = 1 h the instrument cluster transmits the request for evaporator drying via the interior CAN to the automatic air conditioning control and operating unit, which starts evaporator drying. To this end, the blower is activated at the lowest setting for t = 30 min.

The automatic air conditioning control and operating unit actuates the blower regulator. The blower regulator actuates the blower motor at the lowest blower stage.

Function sequence for residual heat utilization (with CODE 581 (Comfort automatic air conditioning) or with CODE 965 (Electrical preinstallation for rental vehicle))

The function is switched on by pressing the "REST" button (with CODE 581 (Comfort automatic air conditioning)) or the "A/C, REST" button (with CODE 965 (Electrical preinstallation for rental vehicle)) on the automatic air conditioning control and operating unit. The automatic air conditioning control and operating unit transmits the request via the interior CAN to the front SAM control unit, which actuates the coolant circulation pump directly. The coolant circulation pump delivers the still warm (residual heat) coolant through the heat exchanger.

The automatic air conditioning control and operating unit actuates the blower regulator. The blower regulator actuates the blower motor at the lowest blower stage. The air drawn in by the blower motor is routed along the heater heat exchanger and thus heated up. The function is terminated after a time of t = 30 min. has elapsed or when the on-board power supply voltage drops below a certain value.

Function sequence for air conditioning shutoff in the event of a crash (as of 01.03.2013)

To prevent the ingress of noxious gases into the vehicle interior in the event of an accident, the automatic air conditioning control and operating unit starts the following activities:

 The blower motors are no longer actuated. Air is not circulated in the vehicle interior.

 The fresh air/recirculated air flap is moved to the recirculated air position. Outside air can no longer enter the vehicle interior.

 The respective refrigerant compressor is switched off.

 The positive temperature coefficient heater booster is switched off.

The supplemental restraint system control unit sends the crash signal via chassis CAN 1, front SAM control unit and interior CAN to the automatic air conditioning control and operating unit.

 Detailed information on actuation of the individual components in the air conditioning is available in the "Actuating the air conditioning components" subfunction.

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

By pressing the "MAX COOL" button on the automatic air conditioning control and operating unit, the blower output is raised to 100% and the temperature is set to "maximum cold".

Function sequence for ram air operation

The speed-dependent ram air flap is adjusted to prevent the air feed in the vehicle interior from increasing when the speed increases. The higher the speed, the further the ram air flap is closed..

The instrument cluster transmits the vehicle speed signal via the interior CAN to the automatic air conditioning control and operating unit. This actuates the fresh air/recirculated air flap actuator motor (except CODE 581 (Comfort automatic air conditioning)) via the climate control LIN depending on the speed. In vehicles with CODE 581 (Comfort automatic air conditioning), the ram air flap actuator motor (up to 31.05.2010) or the fresh air/recirculated air flap actuator motor (as of 01.06.2010) is actuated by the automatic air conditioning control and operating unit via the climate control LIN depending on the speed.