Regulation of Automatic air conditioning, function

P83.40-4503-79

Function requirements, general

 Circuit 15 ON (only circuit 15C or circuit 15R for residual engine heat utilization)

 For cooling operation:

 Engine running

 Refrigerant compressor on (not switched off via the automatic air conditioning control and operating unit)

 The electronic ignition lock control unit transmits the status of circuit 15 to the automatic air conditioning control and operating unit via the interior CAN. The CDI control unit (diesel engine) or the ME-SFI [ME] control unit (gasoline engine) transmits the "Engine running" signal via chassis CAN 1, the electronic ignition lock control unit and the interior CAN to the automatic air conditioning control and operating unit.

Climate control, general

The electronic temperature control and the air distribution in the vehicle interior are dependent on the settings made at the automatic air conditioning control and operating unit and the variables recorded by various sensors (e.g. interior temperature, outside temperature, coolant temperature and 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.

The automatic air conditioning control function encompasses the following functions:

 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 maximum cooling output (with CODE 494 (USA version))

 Function sequence for evaporator drying process

 Function sequence for residual heat utilization

 Function sequence for shutting off A/C after an accident (crash signal transmitted) as of 01.07.2013

Function sequence for recording and evaluating variables

The following variables are recorded and evaluated:

 Outside temperature

 Interior temperature in head area

 Air outlet temperature in rear head area (with CODE 582 (Rear air conditioning system))

 Temperature at the air outlets in the vehicle

 Temperature and moisture of windshield (except CODE 494 (USA version) or with CODE 581 (Comfort automatic air conditioning))

 Coolant temperature

 Temperature on evaporator

 Temperature at evaporator of rear air conditioning (with CODE 582 (Rear A/C system))

 Refrigerant pressure

 Solar radiation

 Air quality (with CODE 581 (Comfort automatic air conditioning))

 Vehicle speed

 Engine speed

 Door status

 Side window position

 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))

 VCS [SBS] status (with CODE 512 (COMAND APS with DVD changer) or CODE 527 (COMAND APS with single DVD drive (with navigation)) or CODE 528 (COMAND incl. DVD changer))

 Settings on RCP [HBF] control unit (with CODE 581 (Comfort automatic air conditioning))

Outside temperature

The outside temperature sensor measures the outside temperature. The SAM control unit reads in the outside temperature sensor signal directly, calculates the outside temperature and sends this via 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.

 The interior temperature is adjusted by actuating the left blend air flap actuator motor for the driver and the right blend air flap actuator motor for the front passenger. The interior temperature in the rear is adjusted by actuating the rear air distribution flap actuator motor.

Interior temperature in head area

The interior temperature is recorded in the head area by the interior temperature sensor with integrated fan. The fan sucks in the air for temperature measurement from the vehicle interior. The signals of the interior temperature sensor with integrated fan are sent by the overhead control panel control unit via roof LIN, SAM control unit and interior CAN to the automatic air conditioning control and operating unit.

Air outlet temperature in rear head area (with CODE 582 (Rear air conditioning system))

The air outlet temperature in the head area in the rear is recorded by the rear air conditioning head area temperature sensor. The signals of the rear air conditioning head area temperature sensor are read in directly by the automatic air conditioning control and operating unit.

Temperature at the air outlets in the vehicle

The temperatures at the air outlets in the vehicle are recorded by the air outlet temperature sensors. 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 sensor are read in directly by the automatic air conditioning control and operating unit.

Temperature and moisture of windshield (except CODE 494 (USA version) or with CODE 581 (Comfort automatic air conditioning))

The vehicle interior humidity and temperature sensor measures the relative humidity and temperature directly at the inside of the windshield and uses this to determine the dew point temperature. The signals of the vehicle interior humidity and temperature sensor are sent via roof LIN, overhead control panel control unit, roof LIN, SAM control unit and interior CAN to the automatic air conditioning control and operating unit. If the windows threaten to fog up, corresponding countermeasures are taken such as, e.g. switching on the refrigerant compressor or starting the engine.

 The left mirror heater (M21/1r1) and right mirror heater (M21/2r1) are switched on when the side windows become fogged.

Coolant temperature

The coolant temperature is recorded by the coolant temperature sensor. The CDI control unit or ME-SFI [ME] control unit reads in the resistance value directly, uses this to calculate the coolant temperature and sends this via chassis CAN 1, electronic ignition lock control unit and interior CAN to the automatic air conditioning control and operating unit. The value is used to control the blend air flaps and to actuate the coolant circulation pump.

Temperature on evaporator

To prevent the evaporator from icing up, the temperature there is measured by the evaporator temperature sensor. The AAC control and operating unit reads in the signal of the evaporator temperature sensor directly.

If the evaporator temperature drops to approx. T = 2 °C, the refrigerant compressor is switched off.

Temperature at evaporator of rear air conditioning (with CODE 582 (Rear A/C system))

To prevent the evaporator of the rear air conditioning from icing up, the temperature there is detected by the rear air conditioning evaporator temperature sensor. The automatic air conditioning control and operating unit reads in the signal of the rear air conditioning evaporator temperature sensor 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 refrigerant pressure sensor signals are read in directly by the automatic air conditioning control and operating unit. The pressure is compared with a stored temperature/pressure curve. At a refrigerant pressure of p < 1.7 bar or p > 30 bar, the respective refrigerant compressor is switched off or not switched in.

Solar radiation

The sun sensor records the intensity of the solar radiation on the vehicle. The AAC control and operating unit reads in the signals from the sun sensor directly and adapts the interior temperature and the blower speed accordingly.

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

Air quality (with CODE 581 (Comfort automatic air conditioning))

The air quality sensor records the concentration of the following noxious gases:

 Carbon monoxide (CO)

 Nitrogen oxides (NOx)

The values are read in directly by the AAC control and operating unit via the climate control LIN. The AAC control and operating unit controls the automatic recirculation according to the 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 speed

The engine speed is read in by the CDI control unit or ME-SFI [ME] control unit and sent via chassis CAN 1, electronic ignition lock control unit and interior CAN to the automatic air conditioning control and operating unit. The engine speed is used among other things to regulate the respective refrigerant compressor.

Door status

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

 Left front door control unit

 Right front door control unit

 Left rear door control unit

 Right rear door control unit

The AAC control and operating unit records the current blower output when the door is open in order to prevent unnecessary readjustment in the event of high temperature differences between the inside and outside air.

Side window position

The position of the respective side window is determined by the following control units and transmitted via 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

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 sliding roof is transmitted by the sliding roof control module via the interior CAN to the automatic air conditioning control and operating unit.

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

VCS [SBS] status (with CODE 512 (COMAND APS with DVD changer) or CODE 527 (COMAND APS with single DVD drive (with navigation)) or CODE 528 (COMAND incl. DVD changer))

The COMAND controller unit sends the status of the VCS [SBS] to the automatic air conditioning control and operating unit via interior CAN. If the VCS [SBS] is active, the blower motor output is restricted by the blower regulator.

Settings on RCP [HBF] control unit (with CODE 581 (Comfort automatic air conditioning))

The climate control of the rear compartment can be set by the rear occupants via the RCP [HBF] control unit. The selected settings are sent by the RCP [HBF] control unit via interior CAN to the automatic air conditioning control and operating unit for processing. These data are used to regulate the air volume, air distribution and temperature in the rear.

Function sequence for AC component actuation

The function sequence for actuating the air conditioning components comprises the following subfunctions:

 Function sequence for actuation of blower motor

 Function sequence for actuation of rear blower motor (with CODE 581 (Comfort automatic air conditioning) and except CODE 582 (Rear air conditioning system))

 Function sequence for actuation of the rear air conditioning system blower motor (with CODE 582 (Rear air conditioning))

 Function sequence for actuation of the air ducting flaps

 Function sequence for actuation of refrigerant compressor

 Function sequence for actuation of the fan motor

 Function sequence for actuation of the PTC heater booster (diesel engine)

 Function sequence for actuation of the rear air conditioning evaporator shutoff valve (with CODE 582 (Rear A/C system))

 Function sequence for actuation of coolant circulation pump

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 via climate control LIN to the blower regulator, which then directly actuates the blower motor.

 The blower motor drives a radial blower which circulates the air in the vehicle interior or which supplies fresh air to the vehicle interior. This prevents the glass panes from fogging up, supplies air to the vehicle occupants and enables pleasant and constant temperatures to be reached quickly in the vehicle interior. Depending on the current settings at the automatic air conditioning control and operating unit, the air is routed through various air ducts and air outlets into the vehicle interior.

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

 MODEL 166 as of 7/1/13
up to model year 2016
The blower motor is switched off in the event of an accident (crash signal sent).

Function sequence for actuation of rear blower motor (with CODE 581 (Comfort automatic air conditioning) and except CODE 582 (Rear air conditioning system))

The rear blower motor is used for better ventilation of the rear compartment. Depending on the settings on the automatic air conditioning control and operating unit and on the RCP [HBF] control unit, the automatic air conditioning control and operating unit forwards the request directly to the booster blower electronic blower regulator, which then actuates the rear blower motor.

 MODEL 166 as of 7/1/13
up to model year 2016
The rear blower motor is switched off in the event of an accident (crash signal sent).

Function sequence for actuation of the rear air conditioning system blower motor (with CODE 582 (Rear air conditioning))

The rear air conditioning blower motor is used to route fresh air or interior air through the rear climate control box into the rear. Depending on the settings on the automatic air conditioning control and operating unit and on the RCP [HBF] control unit, the automatic air conditioning control and operating unit forwards the request via climate control LIN to the rear air conditioning electronic blower regulator, which then actuates the rear air conditioning blower motor.

 MODEL 166 as of 7/1/13
up to model year 2016
The rear air conditioning blower motor is switched off in the event of an accident (crash signal sent).

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.

Vehicles with CODE 580 (Automatic air conditioning):

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

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

 Left and right center air vent flap via left center air vent flap actuator motor (ventilation 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 with blocking function via rear blend air flap actuator motor with blocking function (ventilation control)

 Rear air distribution flap via rear air distribution flap actuator motor

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

Vehicles with CODE 581 (Comfort automatic air conditioning):

 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)

 Rear blend air flap with blocking function via rear blend air flap actuator motor with blocking function (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)

 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 air distribution flap via rear air distribution flap actuator motor

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

The automatic air conditioning control and operating unit actuates the actuator motors via climate control LIN.

 MODEL 166 as of 7/1/13
up to model year 2016
The fresh air/recirculated air flap is closed after an accident (crash signal sent).

 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.

 With circuit 15 OFF, when one of the doors is opened the fresh air/recirculated air flap is moved by the fresh air/recirculated air flap actuator motor to 50 %. This achieves a significant reduction in the door closing forces. The function can be set with the diagnostic tester.

 In order to provide the rear footwell and the air vents in the B-pillars with sufficient air, the opening angle of the rear air distribution flap is limited (opening angle 0 - 50 %).

P83.10-2770-76

P83.10-2903-76

 Additional air outlets are located in the paneling of the B-pillar.

P83.10-2904-76

 MODEL 166.8
up to model year 2016
with CODE 582 (Rear air conditioner)
Additional air outlets are located in the headliner in the rear.

Function sequence for actuation of refrigerant compressor

The refrigerant compressor is responsible for induction and compression of the refrigerant. The refrigerant compressor output is regulated by the compressor control valve of the automatic air conditioning control and operating unit (continuously variable). The automatic air conditioning control and operating unit actuates the compressor control valve directly.

With CODE B09 (Refrigerant compressor with magnetic clutch), a magnetic clutch is also installed. This can be used to completely disconnect the A/C 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 directly actuates the refrigerant compressor with magnetic clutch.

The automatic air conditioning control and operating unit also sends the request for idle speed increase via interior CAN, electronic ignition lock control unit and chassis CAN 1 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 166 as of 7/1/13
up to model year 2016
In the event of an accident (crash signal transmitted), the refrigerant compressor is switched off over the refrigerant compressor regulating valve or over the refrigerant compressor magnetic clutch (with code B09 (Refrigerant compressor with magnetic clutch)).

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 sends the request via interior CAN, electronic ignition lock control unit and chassis CAN 1 to the CDI control unit or the ME-SFI [ME] control unit.

The CDI control unit or the ME-SFI [ME] control unit calculates the target blower speed depending on the engine temperature, compares this with the air conditioning request and then directly actuates the fan motor.

Function sequence for actuation of the PTC heater booster (diesel engine)

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 166 as of 7/1/13
up to model year 2016
The PTC heater booster is switched off in the event of an accident (crash signal transmitted).

Function sequence for actuation of the rear air conditioning evaporator shutoff valve (with CODE 582 (Rear A/C system))

The rear air conditioning evaporator shutoff valve is used to control the infeed of refrigerant to the rear air conditioning evaporator.

Actuation takes place depending on the settings on the automatic air conditioning control and operating unit and on the RCP [HBF] control unit. The automatic air conditioning control and operating unit actuates the rear air conditioning evaporator shutoff valve directly.

Function sequence for actuation of coolant circulation pump

The coolant circulation pump is used for support when the engine is running or, when the residual heat mode is switched on, it pumps the coolant through the heater heat exchanger.

The AAC control and operating unit actuates the coolant circulation pump directly.

Fresh air mode function sequence

The fresh air/recirculated air flap is open 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 includes the following subfunctions:

 Function sequence for air recirculation mode using air recirculation mode button

 Function sequence for pollutant-sensitive air recirculation mode (with CODE 581 (Comfort automatic air conditioning))

Function sequence for air recirculation mode using 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 and the sliding roof (with CODE 414 (Power glass tilting/sliding roof)) or the panoramic sliding sunroof (with CODE 413 (Panoramic glass sunroof with top sliding sunroof)) are closed.

If the air recirculation mode button is then pressed for t > 1.5 s, the side windows, the sliding roof (with CODE 414 (Power glass tilting/sliding roof)) or the panoramic sliding sunroof (with CODE 413 (Panoramic glass sunroof with top sliding sunroof)) 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".

Additional function requirements for pollutant-controlled air recirculation mode (with CODE 581 (Comfort automatic air conditioning))

 Refrigerant compressor SWITCHED ON

Function sequence for pollutant-sensitive air recirculation mode (with CODE 581 (Comfort automatic air conditioning))

The air quality sensor records the pollutant levels of the outside air. The automatic air conditioning control and operating unit reads in the signals of the air quality 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. Following this, operation continues with 80 % pollutant-controlled recirculated air and after another t = 10 s, as required, with 100 % pollutant-controlled recirculated air.

 The pollutant-controlled air recirculation mode is not shown via the LED of the air recirculation mode button.

Function sequence for defroster function

When the defroster button is pressed, all air flaps are closed with the exception of the defroster flaps and the fresh air/recirculated air flap. These are fully opened. Feedback is provided by the LED integrated into the switch lighting up. The defroster flaps are adjusted so that the maximum air flow is directed to the windshield and the front side windows. The blend air flap is set to full warm air supply. The automatic air conditioning control and operating unit regulates the blower regulator and this in turn regulates the blower motor via climate control LIN such that an optimum defrost mode is achieved depending on the outflow air temperature.

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.

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

Pressing the "MAX COOL" button causes the blower output to be raised to 100 % and the specified temperature set to "maximum cold". Feedback is provided by the LED integrated into the switch lighting up.

"MAX COOL" is shown on the display.

Additional function requirements for evaporator drying process

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

 Outside temperature T > 20 °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. The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" signal via chassis CAN 1, electronic ignition lock control unit and interior CAN to the instrument cluster.

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

The automatic air conditioning control and operating unit sends the request via climate control LIN to the blower regulator. The blower regulator actuates the blower motor at the lowest blower stage.

Function sequence for residual heat utilization

Pressing the "REST" button" (with CODE 581 (Comfort automatic air conditioning) and except CODE 494 (USA version)) or the "A/C REST" button" (except CODE 581 (Comfort automatic air conditioning) and except CODE 494 (USA version) or with CODE 581 (Comfort automatic air conditioning) and CODE 582 (Rear air conditioning) and except CODE 494 (USA version)) on the automatic air conditioning control and operating unit switches the function on. The AAC control and operating unit actuates the coolant circulation pump directly.

The coolant circulation pump delivers the still warm (residual heat) coolant through the heat exchanger. At the same time, the automatic air conditioning control and operating unit sends the ventilation request via climate control LIN to the blower regulator, which then actuates the blower motor at reduced power.

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 electrical system voltage drops below a certain value.

Function sequence for shutting off A/C after an accident (crash signal transmitted) as of 01.07.2013

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 refrigerant compressor control valve is switched off. The refrigerant compressor no longer circulates the refrigerant.

 The refrigerant compressor magnetic clutch is opened (with CODE B09 (Refrigerant compressor with magnetic clutch)). The refrigerant compressor is no longer driven.

 The positive temperature coefficient heater booster is switched off.

The supplemental restraint system control unit sends the crash signal via chassis CAN 1, electronic ignition lock 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.