Climate control regulation, function

P83.40-5268-79

P83.40-5268-79

Function requirements, general

 Terminal 15 ON

 Automatic air conditioning switched on

For cooling operation:

 Engine runs

 Refrigerant compressor switched on (without CODE B09 (Refrigerant compressor with magnetic clutch))

 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 over the interior CAN to the automatic air conditioning control and operating unit. The "Engine running" signal is sent by the CDI control unit or the ME-SFI [ME] control unit via chassis CAN 1 (as of 01.03.2016) or chassis CAN (up to 29.02.2016), front SAM control unit and interior CAN to the automatic air conditioning control and operating unit.

Climate control, general

Electronic control of the temperature and air distribution in the vehicle interior is performed depending on the selected settings on the automatic air conditioning control and operating unit and the variables recorded by various sensors (e.g. interior temperature, outside temperature, coolant temperature, vehicle speed).

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 climate control regulation 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 maximum cooling output (with CODE 494 (USA version))

 Function sequence for evaporator drying process

 Function sequence for residual heat utilization (without code 494 (USA version))

 Function sequence for shutoff of the air conditioning system after an accident (crash signal transmitted) as of 01.06.2013

Function sequence for recording and evaluating variables

In addition to the settings made at the automatic air conditioning control and operating unit, the following variables are recorded and evaluated:

 Outside temperature

 Interior temperature

 Temperature at air outlet in vehicle

 Temperature and humidity on windshield (with code B03 (ECO start/stop function))

 Coolant temperature

 Temperature on evaporator

 Refrigerant pressure

 Solar radiation (with code 581 (Automatic air conditioning))

 Air quality (with code 581 (Automatic air conditioning))

 Vehicle speed

 Engine speed

 Door status

 Side window position

 Position of Vario roof

 Voice control system (VCS [SBS]) status (as of 01.03.2016 with code 531 (COMAND APS), up to 29.02.2016 with code 512 (COMAND APS with DVD changer) or code 527 (COMAND APS with single DVD drive (with navigation)))

Outside temperature

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

Head area:

The interior temperature 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 over the wiper/inside rearview mirror-LIN, front SAM control unit and the interior CAN to the automatic air conditioning control and operating unit. The fan sucks in the air for temperature measurement from the vehicle interior.

Instrument panel (with code 581 (Automatic air conditioning)):

The interior temperature is measured in the area of the instrument panel via interior temperature sensor. The signals of the interior temperature sensor are read in directly by the automatic air conditioning control and operating unit. The fan integrated into the interior temperature sensor sucks in the air for temperature measurement from the vehicle interior.

 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. This mean value together with the value of the outside temperature is compared against a characteristic map stored permanently in the automatic air conditioning control and operating unit, and used to regulate the interior temperature.

The regulated 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 operating at the set specified temperature.

Temperature at air outlet in vehicle

Without code 581 (Automatic air conditioning):

The temperature at the air outlet in the left footwell is recorded by the left footwell vent air outlet temperature sensor. The automatic air conditioning control and operating unit regulates the air outlet temperature. The left footwell vent air outlet temperature sensor signal is read in directly by the automatic air conditioning control and operating unit.

With code 581 (Automatic air conditioning):

The temperature at the air outlets in the left and right footwell is recorded by the left footwell vent air outlet temperature sensor and the right footwell vent 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.

Temperature and humidity on windshield (with code B03 (ECO start/stop function))

The vehicle interior humidity/temperature sensor measures the relative air humidity and temperature directly at the inside of the windshield and uses this to determine the dew point temperature.

The signals from the vehicle interior humidity/temperature sensor are read in directly by the front SAM control unit over the wiper/inside rearview mirror-LIN. The front SAM control unit sends the signals over the interior CAN to the automatic air conditioning control and operating unit.

If the windows threaten to fog up, corresponding measures are taken such as, e.g. starting the engine or switching on the A/C compressor.

Coolant temperature

The coolant temperature is recorded by the coolant temperature sensor. The CDI control unit or the ME-SFI [ME] control unit directly reads in the resistance value of the sensor, uses it to calculate the coolant temperature and sends this via chassis CAN 1 (as of 01.03.2016) or chassis CAN (up to 29.02.2016), front SAM control unit and interior CAN to the automatic air conditioning control and operating unit. The value is used to control the blend air flap or the blend air flaps and for actuation of the coolant circulation pump.

 With code 581 (Automatic air conditioning), the interior temperature is changed by separately adjusting the air duct flaps via the left blend air flap actuator motor for the driver and the right blend air flap actuator motor for the front passenger.
Without code 581 (Automatic air conditioning), the air duct flap for the driver and front passenger is adjusted by the blend air flap actuator motor.

Temperature on evaporator

To prevent the evaporator from icing up, the temperature there is recorded by the evaporator temperature sensor. The evaporator temperature sensor signals are read in directly by the automatic air conditioning control and operating unit.

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 signals from the refrigerant pressure sensor are read in directly by the front SAM control unit, and sent over 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 of approx. p < 1.7 bar and p > 30 bar, the refrigerant compressor is switched off or not activated.

Solar radiation (with code 581 (Automatic air conditioning))

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 the blower speed are adapted in accordance with 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.

Air quality (with code 581 (Automatic air conditioning))

The air quality sensor records the following environmental influences:

 Carbon monoxide (CO) concentration level

 Nitrogen oxide (NOx) concentration level

 Outside dew point temperature

 Relative humidity

 Outside temperature

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

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 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 engine speed via chassis CAN 1 (as of 01.03.2016) or chassis CAN (up to 29.02.2016), front SAM control unit and 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 (open or closed) is determined by the following control units and sent over the interior CAN to the automatic air conditioning control and operating unit:

 Left door control unit

 Right door 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 interior CAN to the AAC control and operating unit:

 Left door control unit

 Right door control unit

Position of Vario roof

The position of the Vario roof is sent by the vario roof control control unit over the interior CAN to the automatic air conditioning control and operating unit.

Voice control system (VCS [SBS]) status (as of 01.03.2016 with code 531 (COMAND APS), up to 29.02.2016 with code 512 (COMAND APS with DVD changer) or code 527 (COMAND APS with single DVD drive (with navigation)))

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

Function sequence for AC component actuation

Activation of the AC 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 refrigerant compressor

 Function sequence for actuation of combustion engine fan motor and air conditioning with integrated control

 Function sequence for actuation of coolant circulation pump

Function sequence for actuation of blower motor

The through-ventilation of the vehicle interior is achieved with the support of the blower motor. The AAC control and operating unit transmits the request to the blower regulator via the climate control LIN, which then 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 windows from fogging up, supplies air to the vehicle occupants and allows 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.

 In vehicles as of 01.06.2013, the blower motor is switched off after an accident (crash signal transmitted).

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 without code 581 (Automatic air conditioning):

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

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

 Center air vent flap over the center air vent flap actuator motor (ventilation control)

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

Vehicles with CODE 581 (Automatic air conditioning):

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

 Center air vent flap over the center air vent flap actuator motor (ventilation control)

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

 The defroster flap actuator motor also operates the footwell flap in addition to the defroster flap through kinematics.

 In vehicles as of 01.06.2013, the fresh air/recirculated air flap is closed after an accident (crash signal transmitted).

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

 At circuit 15 Off, the fresh air/recirculated air flap is adjusted by the fresh air/recirculated air flap actuator motor when one of the doors is opened to a partial recirculated air position. The door closing forces are thereby reduced. The function can be set with the diagnostic tester.

P83.10-2763-75

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 continuously up to 100 % by the automatic air conditioning control and operating unit through the refrigerant compressor control valve. The automatic air conditioning control and operating unit sends the request to switch on the A/C compressor over the interior CAN to the front SAM control unit. This receives the request and actuates the refrigerant 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 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 sends the request for the idle speed increase via interior CAN, front SAM control unit and chassis CAN 1 (as of 01.03.2016) or chassis CAN (up to 29.02.2016) to the CDI control unit or the ME-SFI [ME] control unit. This increases the idle speed in accordance with the additional load that occurs when the refrigerant compressor is switched on.

 In vehicles as of 01.06.2013, the refrigerant compressor is shut off after an accident (crash signal sent) 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 combustion engine fan motor and air conditioning with integrated control

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 interior CAN, front SAM control unit and chassis CAN 1 (as of 01.03.2016) or chassis CAN (up to 29.02.2016) to the CDI control unit or the ME-SFI [ME] control unit. The CDI control unit or the ME-SFI [ME] control unit then calculates the nominal fan speed as a function of the engine temperature, compares this against the request from the automatic air conditioning control and operating unit, and then actuates the fan motor accordingly.

Function sequence for actuation of coolant circulation pump

The coolant circulation pump supports the coolant circuit, e.g. at low engine speeds or when the residual heat utilization function is used.

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 then directly actuates the coolant circulation pump.

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 encompasses 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 (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 light-emitting diode (LED) above the air recirculation mode button is illuminated during the 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 are closed. The request for this is sent by the automatic air conditioning control and operating unit via interior CAN to the following control units:

 Left door control unit

 Right door control unit

If the air recirculation mode button is then pressed for t < 1.5 s, the side windows are moved back to the default position (insofar as they were not manually adjusted during the air recirculation mode).

 Detailed information on the convenience feature function is available in a separate document.

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

 Refrigerant compressor switched on (without CODE B09 (Refrigerant compressor with magnetic clutch))

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

 Defrost mode not active

Function sequence for pollutant-sensitive air recirculation mode (with code 581 (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, the air recirculation flap is closed to 80 % and then after another t = 10 s as required to 100 %.

 The pollutant-controlled air recirculation mode is not indicated by the LED in the air recirculation mode button.

Function sequence for defroster function

Operating the Defrost button on the automatic air conditioning control and operating unit closes all air duct flaps with the exception of the defroster flap and the fresh air/recirculated air flap. These are fully opened. The defroster flap is 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 blower motor is actuated by the automatic air conditioning control and operating unit over the blower regulator to ensure the best possible defrost mode depending 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 and then heated up to the maximum temperature.

 With code 581 (Automatic air conditioning), the warm air supply for the defrost mode occurs separately by adjusting the air duct flaps using the left blend air flap actuator motor for the driver and using the right blend air flap actuator motor for the front passenger. Without code 581 (Automatic air conditioning), the air duct flap for the driver and front passenger is adjusted by the blend air flap actuator motor.

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

Pressing the "MAX COOL" button on the automatic air conditioning control and operating unit increases the blower output to 100 %. The nominal temperature values are regulated to "maximum cooling". "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 > 18 °C

 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 all windows when starting the air conditioning, an evaporator drying process is performed. The timer is activated in the instrument cluster when the engine is switched off. 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 ventilation is activated at the lowest setting for t = 30 min.

The automatic air conditioning control and operating unit sends the corresponding request via climate control LIN to the blower regulator. The blower regulator then actuates the blower motor directly.

Function sequence for residual heat utilization (without code 494 (USA version))

Operating the "REST" button (without code 581 (Automatic air conditioning)) or the "A/C REST" button (with code 581 (Automatic air conditioning)) on the automatic air conditioning control and operating unit switches on the function. The automatic air conditioning control and operating unit sends the request over the interior CAN to the front SAM control unit, which then actuates the coolant circulation pump. 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 via the climate control LIN at the same time, which then actuates the blower motor at a low 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. Depending on the outside temperature, the Vario roof status and the heat/cool request, the air is routed over the following openings into the vehicle interior:

 Defroster vents

 Center outlets

 Footwell vents

 The function can also be used in summer as ventilation feature. In this instance (cooling case) the coolant circulation pump is not actuated. The vehicle is ventilated with fresh outside air.

Function sequence for shutoff of the air conditioning system after an accident (crash signal transmitted) as of 01.06.2013

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 motor is 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 regulating valve (without code B09 (Refrigerant compressor with magnetic clutch)) is switched off. The refrigerant compressor no longer circulates the refrigerant.

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

The crash signal is sent by the supplemental restraint system control unit via chassis CAN 1 (as of 01.03.2016) or chassis CAN (up to 29.02.2016), 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 A/C components" chapter.