Climate control regulation, function

P83.40-5139-79

Function requirements, general

For regulating the climate control:

 Terminal 15 ON

 Automatic air conditioning switched on

For cooling operation:

 Engine running (except for hybrid vehicles)

 Refrigerant compressor switched on (not switched off via the climate control control unit)

For evaporator drying process:

 Engine Off

For residual heat utilization (with code 228 (Stationary heater) or code 581 (Automatic air conditioning) or code 965 (Taxi/rental car pre-installation) or for hybrid vehicles):

 Terminal 15 Off or terminal 15C Off

 The electronic ignition lock control unit sends the status of terminal 15 via interior CAN to the A/C control unit.

 The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" signal over the drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and the interior CAN to the climate control control unit.

Climate control, general

The electronic temperature control and the air distribution in the vehicle interior take place depending on the settings selected at the climate control operating unit, the rear air conditioning operating unit (with code 581 (Automatic air conditioning)) or in the head unit and the variables (e. g. interior temperature, outside temperature, coolant temperature, vehicle speed) recorded by various sensors.

The A/C control unit is networked over the interior CAN, climate control LIN 1, climate control LIN 2 and the A/C operating unit LIN to the vehicle electronics. This in turn makes it possible to incorporate relevant parameters in order to improve regulation quality and to lower power consumption.

The climate control regulation function encompasses the following subfunctions:

 Recording and evaluation of variables

 Actuation of air conditioning components

 Shift point adjustment (transmission 725 and except for hybrid vehicles)

 Fresh air mode

 Recirculated air mode

 Defrost

 Evaporator drying

 Residual heat utilization (with code 228 (Stationary heater) or code 581 (Automatic air conditioning) or code 965 (Taxi/rental car pre-installation) or for hybrid vehicles)

 Shutoff of air conditioning after an accident (crash signal sent)

Recording and evaluation of variables

The following variables are recorded and evaluated:

 Outside temperature

 Interior temperature in head area

 Temperature at the air outlets in the vehicle

 Temperature and moisture on windshield

 Coolant temperature

 Evaporator temperature

 Refrigerant pressure

 Solar radiation

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

 Vehicle speed

 Engine speed

 Door status

 Position of side windows

 Position of sliding roof (with code 414 (Sliding roof)) or panoramic sliding sunroof (with code 413 (Panoramic sliding sunroof))

 Operating settings

 Status of voice control system (VCS) (with 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 it to the A/C control unit over the interior CAN. The climate control control unit regulates the interior temperature according to the outside temperature by adjusting the blend air flaps.

 If the vehicle is stationary, the measured temperature can differ considerably from the actual outside temperature. The outside temperature is only included in the regulation of the vehicle interior temperature when the vehicle speed for a period of at least 30 s is higher than 30 km/h. At speeds < 30 km/h as well as when switching the ignition on and off, the last measured temperature value is then used.

Interior temperature in head area

The interior temperature in the head area is recorded by the interior temperature sensor with the integrated fan that is incorporated into the overhead control panel control unit. The integrated fan of the interior temperature sensor draws the air for temperature measurement out of the vehicle interior. The overhead control panel control unit reads in the value of the interior temperature and transmits this via the interior CAN to the climate control control 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 signals from the air outlet temperature sensors are read in directly by the climate control control unit. The A/C system control unit regulates the air outlet temperature at each of the air outlets.

Temperature and moisture on windshield

A humidity and temperature sensor is integrated in the rain/light sensor with additional functions. This sensor measures the relative air humidity and temperature directly at the inside of the windshield. These values are used by the rain/light sensor with additional functions to calculate the dew point temperature. Comparison of the windshield surface temperature with the dew point temperature enables impending fogging of the windows to be detected.

The rain/light sensor with additional functions sends the dew point temperature via the rain/light sensor LIN, front SAM control unit and interior CAN to the climate control control unit.

If the probability of window fogging is high, the climate control control unit increases the blower setting. If the automatic ECO start/stop function is active, the climate control control unit can prevent an automatic engine stop. In the case of impending window fogging during an engine stop phase, the climate control control unit can cause the engine to start and the refrigerant compressor to switch in.

Coolant temperature

The coolant temperature is calculated 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 coolant temperature via the drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and interior CAN to the climate control control unit.

The coolant temperature is used to control the blend air flaps and to actuate the coolant circulation pump.

In hybrid vehicles, the coolant temperature in the high voltage PTC heater is also measured by the high voltage PTC heater temperature sensor. The climate control control unit reads in the signals of the high-voltage PTC heater temperature sensor over the climate control LIN 2. The value is used to control the coolant circulation pump.

Evaporator temperature

The temperature at the evaporator is recorded by the evaporator temperature sensor. The A/C control unit reads in the signals from the evaporator temperature sensor directly. If the evaporator temperature drops to approx. 2 °C, the refrigerant compressor is switched off or the front evaporator shutoff valve (for hybrid vehicles) is closed. This serves to prevent the evaporator from icing up. Above an evaporator temperature of 2.5 °C, the refrigerant compressor is switched on again or the front evaporator shutoff valve (for hybrid vehicles) is opened again.

The evaporator temperature is held for a maximum of 20 minutes at 2.5 °C. The evaporator temperature is then (depending on cooling requirements) adjusted in a range of 3 to 8 °C.

Refrigerant pressure

The refrigerant pressure is recorded by the refrigerant pressure sensor. The climate control control unit reads in the signals from the refrigerant pressure sensor directly. The pressure is compared with a stored temperature/pressure curve. At a refrigerant pressure < 0.8 or > 28 bar, the refrigerant compressor is switched off or not switched on.

Solar radiation

A sun sensor (2-quadrant sensor) is integrated in the rain/light sensor with additional functions. The sun sensor detects the angle of incidence and the intensity of the solar radiation entering the left and right side of the vehicle. The rain/light sensor with additional functions sends this information via the rain/light sensor LIN, front SAM control unit and interior CAN to the climate control control unit. The climate control control unit then regulates the interior temperature accordingly. For example, in the event of one-sided solar radiation, an appropriate temperature difference is set between the left and the right specified control temperatures.

If the sun is shining into the vehicle from the side or from the rear and additionally at an acute angle, the sun sensor at the windshield would deliver imprecise values. This is why a sun sensor is virtually realized in the rear passenger compartment. Location information is obtained from GPS data. The position of the sun is deduced from the time of day. The head unit sends the relevant information via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the climate control control unit. The climate control control unit references the values from the sun sensor at the windshield and adapts the temperature control accordingly.

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

The air quality sensor measures the concentration of the following pollutants:

 Carbon monoxide (CO)

 Nitrogen oxides (NOx)

The climate control control unit reads in the signals from the air quality sensor via the climate control LIN 1. If the concentration of pollutant gas is high, the climate control control unit activates air recirculation mode.

Vehicle speed

The vehicle speed is calculated by the instrument cluster. Information about the vehicle speed is transmitted by the instrument cluster via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the climate control control unit. The vehicle speed is used for regulation of the ram air function and for internal calculation of the outside temperature, e.g.  in stationary operation.

Engine speed

The engine speed is calculated by the CDI control unit or the ME-SFI [ME] control unit. The CDI control unit or the ME-SFI [ME] control unit sends the engine speed via the drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and interior CAN to the climate control control unit. The engine speed is used to regulate the refrigerant compressor, among other things.

Door status

The status of each door (open or closed) is determined by the following control units and sent via the interior CAN to the climate control control unit:

 Left front door control unit

 Right front door control unit

 Left rear door control unit

 Right rear door control unit

If the door is open, the climate control control unit references the values from the interior temperature sensor with integrated fan and adapts the temperature control accordingly. If there is a large difference in temperature between the interior air and outside air, unnecessary readjustment is avoided.

Position of side windows

The position of the side windows is determined by the following control units and sent via the interior CAN to the climate control control unit:

 Left front door control unit

 Right front door control unit

 Left rear door control unit

 Right rear door control unit

If the side windows are open, the climate control control unit references the values from the interior temperature sensor with integrated fan and adapts the temperature control accordingly. If there is a large difference in temperature between the interior air and outside air, unnecessary readjustment is avoided.

Position of sliding roof (with code 414 (Sliding roof)) or panoramic sliding sunroof (with code 413 (Panoramic sliding sunroof))

The position of the sliding roof is transmitted by the sliding roof control module to the A/C control unit via the interior CAN. The position of the panoramic sliding sunroof is transmitted by the panoramic sliding sunroof control unit to the A/C control unit via the interior CAN.

If the sliding roof or panoramic sliding sunroof is open, the climate control control unit references the values from the interior temperature sensor with integrated fan and adapts the temperature control accordingly. If there is a large difference in temperature between the interior air and outside air, unnecessary readjustment is avoided.

Operating settings

The settings for climate control of the vehicle interior can be made at the following control points:

 Climate control operating unit

 Rear air conditioning operating unit (with code 581 (Automatic air conditioning))

 Head unit

 VCS (with code 531 (COMAND APS))

Climate control operating unit

The climate control operating unit has the following buttons which are used for making the various settings:

 Left temperature selection button

 Air recirculation mode button

 Climate control and residual heat ON/OFF menu button (with code 228 (Stationary heater) or code 581 (Automatic air conditioning) or for hybrid vehicles)

 Right temperature selection button

 Left air distribution button (with CODE 581 (Automatic air conditioning))

 "SYNC" button (with code 580 (Air conditioning) or code 965 (Taxi/rental car pre-installation))

 "A/C" button (with code 580 (Air conditioning) or code 581 (Automatic air conditioning) except code 228 (Stationary heater) or for hybrid vehicles)

 Right air distribution button (with CODE 581 (Automatic air conditioning))

 "A/C" and residual heat ON/OFF button (with code 965 (Taxi/rental car pre-installation))

 Blower button, front

 AUTO button, front

 Defrosting button

 Air distribution button (with code 580 (Air conditioning) or code 965 (Taxi/rental car pre-installation))

 Auxiliary climate control button (for hybrid vehicles)

 "OFF" button and climate control menu (with code 580 (Air conditioning) or code 965 (Taxi/rental car pre-installation))

The climate control operating unit sends information regarding the settings via the climate control LIN to the climate control control unit. This data is used to regulate the air flow, air distribution and interior temperature. The selected settings are additionally displayed on the Audio/COMAND display. For this purpose, the climate control control unit sends the relevant information via the interior CAN, the electronic ignition lock control unit and the user interface CAN to the head unit. The head unit generates the corresponding image data, transmits a switch-on request via the telematics CAN to the audio/COMAND display and transfers the image data via the HSVL line to the audio/COMAND display. For feedback on the function, the A/C control unit transmits the request for LED actuation via the climate control LIN to the climate control operating unit.

 The air conditioning system or the refrigerant compressor can be switched off if the "A/C" button, the "OFF" button and the climate control menu or the "A/C" and residual heat ON/OFF button is installed. If these buttons are not installed, it can be switched off via the menu in the head unit.

Rear air conditioning operating unit (with code 581 (Automatic air conditioning))

Settings for climate control in the rear compartment can be made at the rear air conditioning operating unit. The rear air conditioning operating unit sends information regarding the settings via the climate control LIN to the climate control control unit. This data is used to regulate the air volume and the temperature in the rear compartment. The settings are shown in the display of the rear air conditioning operating unit.

Head unit

The menu in the head unit can be used to switch off the air conditioning system or to select the climate control function. The head unit sends the relevant information via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the climate control control unit. The head unit generates the corresponding image data, transmits a switch-on request via the telematics CAN to the audio/COMAND display and transfers the image data via the HSVL line to the audio/COMAND display.

VCS (with code 531 (COMAND APS))

The VCS can be used for controlling the following air conditioning functions by means of voice input:

 The air conditioning system / refrigerant compressor can be switched on/off

 The synchronization function can be switched on/off (with code 580 (Air conditioning system) or code 965 (Taxi/rental car pre-installation))

 Ionization can be switched on/off (with code P21 (Air quality package))

 The perfume atomizer can be switched on/off and set (with code P21 (Air quality package))

 The defrost function can be switched on/off

 The automatic air conditioning can be switched on/off

 Air recirculation mode can be switched on/off

 The climate style can be set (with code 581 (Automatic air conditioning))

 The interior temperature can be set

 The air distribution can be set

 The air flow can be set

The VCS is integrated in the head unit. The head unit sends the relevant information via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the climate control control unit.

Status of the VCS (with code 531 (COMAND APS))

When the VCS is active, the output of the electronic blower motor is limited by the climate control control unit. The head unit sends the status of the VCS over the user interface CAN, electronic ignition lock control unit and the interior CAN to the A/C control unit.

Actuation of air conditioning components

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

 Actuation of electronic blower motor

 Actuation of electronic booster blower (with code 581 (Automatic air conditioning))

 Actuation of air ducting flaps

 Actuation of refrigerant compressor (except for hybrid vehicles)

 Actuation of electric refrigerant compressor (for hybrid vehicles)

 Actuation of fan motor (engine fan)

 Actuation of PTC heater booster (engine 654, 642 or 274 with code 401 (Seat climate control for driver and front passenger) or code 824 (Additional parts for countries with cold temperatures) or code 873 (Seat heating for driver and front passenger) or code 902 (Seat heating Plus for driver and front passenger) except code 228 (Stationary heater) or code 913 (Hot countries code) or for hybrid vehicles)

 Actuation of high voltage PTC heater (for hybrid vehicles)

 Actuation of high voltage PTC heater switchover valve (for hybrid vehicles)

 Actuation of front evaporator shutoff valve (for hybrid vehicles)

 Actuation of coolant circulation pump

 Actuation of driver side air vent ionizer (with code P21 (Air quality package))

 Actuation of perfume atomizer generator (with code P21 (Air quality package))

 Actuation of high-voltage battery cooling expansion valve (for hybrid vehicles)

Actuation of electronic blower motor

Ventilation of the vehicle interior is achieved with the aid of the electronic blower motor. The climate control control unit actuates the electronic blower motor via climate control LIN 2.

 The electronic blower motor drives a radial blower which circulates the air in the vehicle interior or 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 climate control operating unit, the air is distributed via various air ducts and air outlets in the vehicle interior.

 Model 213
with code 531 (COMAND APS)
except code 1U6 (R744 refrigerant)
With VCS [SBS] active, the blower setting is reduced.

 The electronic blower motor is switched off in the event of an accident (crash signal transmitted).

Actuation of electronic booster blower (with code 581 (Automatic air conditioning))

The electronic booster blowers improve ventilation of the rear compartment. The climate control control unit actuates the electronic booster blowers via climate control LIN 2. Actuation takes place depending on the settings made at the rear air conditioning operating unit.

 If the electronic booster blowers are switched on, the electronic blower motor is also actuated.

 The electronic booster blowers are switched off following an accident (crash signal sent).

Actuation of air ducting flaps

The air distribution in the vehicle interior is controlled by adjusting the air ducting flaps in the air conditioner housing. The following components are actuated by the A/C control unit via climate control LIN 1:

Vehicles with CODE 580 (Air conditioning):

 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)

 Fresh air/ram air/air recirculation flap over fresh air/ram air/air recirculation flap actuator motor (fresh air/ram air/air recirculation control)

 Defroster/footwell/center air vent flap over defroster/footwell/center air vent flap actuator motor (ventilation control)

 The position of the defroster/footwell/center air vent flap is detected by the central air distribution position detection microswitch. The climate control control unit reads in the status of the central air distribution position detection microswitch directly. If an incorrect position is detected, the position of the defroster/footwell/center air vent flap is readjusted by the A/C control unit via the defroster/footwell/center air vent flap actuator motor.

Vehicles with CODE 581 (Automatic air conditioning):

 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 footwell/center air vent/side air vent and rear air vent flap via the left footwell/center air vent/side air vent and rear air vent flap actuator motor (ventilation control)

 Right footwell/center air vent and side air vent flap via the right footwell/center air vent and side air vent flap actuator motor (ventilation control)

 Fresh air/ram air/air recirculation flap over fresh air/ram air/air recirculation flap actuator motor (fresh air/ram air/air recirculation control)

 Defroster flap via the defroster/footwell/center air vent 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)

P83.10-2916-79

 Model 213
with code 581 (Automatic air conditioning)
except code 1U6 (R744 refrigerant)
There are additional air outlets in the B-pillar trim.

Actuation of refrigerant compressor (except for hybrid vehicles)

The refrigerant compressor is responsible for induction and compression of the refrigerant. The refrigerant compressor is continuously output-controlled up to 100 % by the climate control control unit through the refrigerant compressor regulation valve. The A/C system control unit actuates the refrigerant compressor regulating valve directly.

On vehicles 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 A/C control unit directly actuates the refrigerant compressor with magnetic clutch.

In addition, the climate control control unit sends the calculated torque of the refrigerant compressor via the interior CAN, electronic ignition lock control unit, chassis FlexRay, powertrain control unit and drivetrain CAN to the CDI control unit or to the ME-SFI [ME] control unit. This keeps the idle speed constant in accordance with the additional load that occurs when the refrigerant compressor is switched on.

The refrigerant compressor is switched off under the following conditions:

 Refrigerant pressure below 0.8 bar

 Refrigerant pressure above 28 bar

The refrigerant compressor is switched on under the following conditions:

 Refrigerant pressure over 0.9 bar

 Refrigerant pressure below 27 bar

 In the event of an accident (crash signal transmitted), the refrigerant compressor is switched off via the refrigerant compressor regulating valve or via the refrigerant compressor magnetic clutch (with code B09 (Refrigerant compressor with magnetic clutch)).

Actuation of electric refrigerant compressor (for hybrid vehicles)

The electric refrigerant compressor is responsible for intake and compression of the refrigerant. The electric A/C compressor is actuated by the A/C control unit over the climate control LIN 2.

 The control unit and power electronics for the refrigerant compressor and the electric motor for the refrigerant compressor are integrated into the electric refrigerant compressor.

 In the event of an accident (crash signal sent), the electric refrigerant compressor is switched off.

 If the high-voltage battery overheats, the battery management system control unit sends a request for cooling over the hybrid CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and the interior CAN to the climate-control control unit, which then actuates the electric refrigerant compressor over the climate control LIN 2. The A/C control unit sends feedback the opposite way to the battery management system control unit.

Actuation of fan motor (engine fan)

The fan motor is used for cooling the coolant and refrigerant. The climate control control unit calculates the target fan speed according to the refrigerant pressure and sends the speed via the interior CAN, electronic ignition lock control unit, chassis FlexRay, powertrain control unit and engine CAN to the CDI control unit or to the ME-SFI [ME] control unit.

The CDI control unit or the ME-SFI [ME] control unit corrects the requested target fan speed to match the engine temperature and actuates the fan motor accordingly.

Actuation of PTC heater booster (engine 654, 642 or 274 with code 401 (Seat climate control for driver and front passenger) or code 824 (Additional parts for countries with cold temperatures) or code 873 (Seat heating for driver and front passenger) or code 902 (Seat heating Plus for driver and front passenger) except code 228 (Stationary heater) or code 913 (Hot countries code) or for hybrid vehicles)

When required, the PTC heater booster is switched on by the A/C control unit over the climate control LIN 2. As a result, the vehicle interior is heated up more quickly.

 The PTC heater booster is switched off in the event of an accident (crash signal transmitted).

Actuation of high voltage PTC heater (for hybrid vehicles)

When required, the high voltage PTC heater is switched on by the climate control control unit over the climate control LIN 2. As a result, the vehicle interior is heated up more quickly. To protect the high-voltage PTC heater against damage, it is switched off at a water temperature of 90 °C. The water temperature is recorded by the high voltage PTC heater temperature sensor, and read in by the climate control control unit over the climate control LIN 2.

 The high-voltage PTC heater is switched off in the event of an accident (crash signal sent).

 In the event of an accident, the high-voltage components are switched off by the battery management system control unit.

Actuation of high voltage PTC heater switchover valve (for hybrid vehicles)

The high voltage PTC heater switchover valve regulates the flow of coolant to the heater heat exchanger (actuated by high voltage PTC heater switchover valve) or to the engine and the heater heat exchanger (small or large coolant circuit). The climate control control unit sends the request to actuate the high-voltage PTC heater switchover valve via climate control LIN 2 to the high-voltage PTC heater. The high-voltage PTC heater actuates the high-voltage PTC heater switchover valve directly.

Actuation of front evaporator shutoff valve (for hybrid vehicles)

The front evaporator shutoff valve consists of a mechanical expansion valve and a shutoff valve that is directly actuated by the climate control control unit.

The front evaporator shutoff valve is used to control the flow of refrigerant to the evaporator. The climate control control unit actuates the evaporator shutoff valve directly.

Actuation of coolant circulation pump

The coolant circulation pump is used to support the coolant circuit. The heated coolant passes through the heater heat exchanger, which dissipates heat to the air blowing by. At a low engine speed, during engine stop or during electric mode (for hybrid vehicles), the coolant circulation pump is also actuated in order to ensure that the flow volume required to heat the blowby air is sufficient. The climate control control unit actuates the coolant circulation pump directly.

Additional function requirements for actuation of driver side air vent ionizer (with CODE P21 (Air quality package))

 Ionization activated

 Blower switched on

 Climate control active

Actuation of driver side air vent ionizer (with code P21 (Air quality package))

The driver side air vent ionizer is used for ionization of the air in the vehicle interior. The air is cleaned and freshened by means of ionization. The ionization of the interior air itself is odor-neutral and cannot be detected directly as such in the vehicle.

The head unit transmits the "Switch on ionization" request via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the climate control control unit. The A/C control unit actuates the driver side air vent ionizer via climate control LIN 2.

Additional function requirements for actuation of perfume atomizer generator (with CODE P21 (Air quality package))

 Perfume atomization activated

 Glove compartment CLOSED

 Flask inserted

 Climate control active

 The status of the glove compartment (open or closed) is sensed by the glove compartment lamp switch. The perfume atomizer alternator directly reads in the status of the glove compartment switch.

Actuation of perfume atomizer generator (with code P21 (Air quality package))

The perfume atomizer generator is used to supply fragrance to the vehicle interior. A fan is installed in the fragrance generator, which produces a flow of purified air. When the vial is inserted and the perfume atomization has been switched on, the air flow is guided over the surface of the fragrance and enriched with scent molecules. This scented air is delivered directly into the vehicle interior through an opening in the diffuser grid (in front of the Audio/COMAND display) and diffuses throughout the vehicle. Perfume atomization is pulsed, i. e. it is active for 5 min after activation and then switches itself off for 5 min. The interval switching is used to prevent the vehicle occupants from getting used to the scent. This maintains the occupants' perception capability of the perfume atomization.

The head unit transmits the "Switch on perfume atomization" request and the "Perfume atomization intensity" request via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the A/C control unit. The A/C control unit actuates the perfume atomizer alternator via climate control LIN 2.

The glove compartment lamp switch sends a ground signal directly to the perfume atomizer generator when the glove compartment is opened. It then switches off active perfume atomization and switches the flask illumination on. The flask in the perfume atomizer generator is also disconnected from the working position and moved to the removal position.

When the glove compartment is closed, the inserted flask is moved to the working position by the perfume atomizer generator with terminal 15 on. The perfume atomizer generator also switches off the flask illumination and activates the last perfume atomization intensity set in the climate control menu of the head unit.

If no flask is inserted in the perfume atomizer generator, the message "Insert perfume atomizer cartridge" appears in the Audio/COMAND display. The perfume atomizer generator recognizes whether a flask was inserted by measuring the power consumption of the integrated motor. If another object is used instead of the flask, the perfume atomizer generator can recognize the object as a flask by mistake.

Actuation of high-voltage battery cooling expansion valve (for hybrid vehicles)

The high-voltage battery cooling expansion valve consists of a mechanical expansion valve and a shutoff valve that is directly actuated by the powertrain control unit.

The powertrain control unit sends the corresponding request via the chassis FlexRay, electronic ignition lock control unit and interior CAN to the climate control control unit.

The powertrain control unit sends the status of the shutoff valve (open/closed) via the chassis FlexRay, electronic ignition lock control unit and via the interior CAN to the climate control control unit.

Shift point adjustment (transmission 725 and except for hybrid vehicles)

If increased cooling or heating is required, the fully integrated transmission control unit can adjust the shift point.

The A/C control unit sends the shift point adjustment request over the interior CAN, electronic ignition lock control unit, chassis FlexRay, powertrain control unit and the drive train CAN to the fully integrated transmission control unit.

Fresh air mode

The fresh air/ram air/air recirculation flap is open during fresh air mode. Fresh air is fed through the air conditioning housing and into the vehicle interior.

The climate control control unit actuates the fresh air/ram air/air recirculation flap actuator motor via climate control LIN 1.

Recirculated air mode

The function sequence for the air recirculation mode encompasses the following subfunctions:

 Air recirculation mode via the air recirculation mode button

 Pollutant-controlled air recirculation mode (with code 581 (Automatic air conditioning))

 Automatic air recirculation mode

Air recirculation mode via the air recirculation mode button

Pressing the air recirculation mode button on the climate control operating unit for less than 1.5 s closes the fresh air/ram air/air recirculation flap to prevent air entering from the outside. The air only circulates in the vehicle interior and unpleasant odors and harmful gases are kept out. The LED in the air recirculation mode button lights up during air recirculation mode.

The climate control operating unit reads in the status of the air recirculation mode button directly and sends the status to the climate control control unit via the climate control LIN. The climate control control unit actuates the fresh air/ram air/air recirculation flap actuator motor via climate control LIN 1 and sends the "air recirculation mode active" status via climate control LIN 1 to the climate control operating unit which actuates the LED in the air recirculation mode button.

The air recirculation mode is switched off automatically:

 After 5 min at outside temperatures below 5 °C

 After 5 min, if cooling with air dehumidification is switched off

 After 30 min at outside temperatures above 5 °C and if cooling with air dehumidification is switched on

Vehicles except code 460 (Canada version) or code 494 (USA version) or code 835 (South Korea vehicles additional parts):

If the air-recirculation mode button is actuated for > 1.5 s, the side windows and the sliding sunroof (with code 414 (Sliding sunroof)) or the panoramic sliding sunroof (with code 413 (Panoramic sliding sunroof)) are closed. If the air recirculation mode button is then pressed for > 1.5 s, the side windows and the sliding roof (with code 414 (Sliding roof)) or the panoramic sliding sunroof (with code 413 (Panoramic sliding sunroof)) are moved back to their default positions (provided that they were not manually adjusted during air recirculation mode).

Additional function requirements for pollutant-sensitive air recirculation mode (with code 581 (Automatic air conditioning))

 Refrigerant compressor switched on

Pollutant-controlled air recirculation mode (with code 581 (Automatic air conditioning))

The air quality sensor sends the outside air pollutant values over the climate control LIN 1 to the A/C control unit. Starting from a certain pollutant concentration, the fresh air/ram 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, after starting the engine, the condition for pollutant-sensitive air recirculation mode is given, fresh air is initially supplied for 30 s. Then 80 % of the pollutant-controlled air recirculation mode is initially used. After 10 s the output is increased as required to the 100 % pollutant controlled air-recirculation mode.

 The pollutant-controlled air-recirculation mode is active for a maximum of 30 minutes and this is not indicated by the LED in the air-recirculation mode button.

Additional function requirements for automatic air recirculation mode

 Automatic air conditioning activated

 Outside temperature above 5 °C (for automatic air recirculation mode in a tunnel)

Automatic air recirculation mode

The air recirculation mode is switched on automatically:

 At high outside temperatures

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 it to the A/C control unit over the interior CAN.

 In a tunnel (with code 531 (COMAND APS))

The head unit sends the GPS data via user interface CAN, electronic ignition lock control unit and interior CAN to the A/C control unit.

The A/C control unit actuates the fresh air/ram air/air recirculation flap actuator motor over the climate control LIN 1 and the fresh air/ram air/air recirculation flap is set to the recirculated air position.

 The automatic air-recirculation mode active for a maximum of 30 minutes and this is not indicated by the LED in the air-recirculation mode button.

Defrost

Operating the defrosting button causes all the air flaps with the exception of the defroster flap and the fresh air/ram air/air recirculation flap to be closed. 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 climate control control unit actuates the electronic blower motor via climate control LIN 2 in such a way that optimum defrost operation is guaranteed depending on the outflowing air temperature.

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.

Additional function requirements for evaporator drying process

 Refrigerant compressor was active at least once during the last ignition cycle

 Evaporator temperature above 3 °C

 Outside temperature above 20 °C

 Doors closed

 Kilometer reading more than 250 km

Evaporator drying

To counteract odors in the vehicle interior and fogging of windows when the air conditioning system is started, evaporator drying is carried out.

After the engine is switched off, the climate control control unit sends the signal to activate the evaporator drying timer via the interior CAN, the electronic ignition lock control unit and the user interface CAN to the instrument cluster. The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" signal over the drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and the interior CAN to the climate control control unit.

After a waiting time of 1  h, the instrument cluster sends the request for evaporator drying via the user interface CAN, electronic ignition lock control unit and interior CAN to the climate control unit, which starts the evaporator drying process. The electronic blower motor is actuated for this at the lowest stage for 30 minutes. The climate control control unit actuates the electronic blower motor via climate control LIN 2. The air supply serves to reduce residual moisture in the evaporator.

Residual heat utilization (with code 228 (Stationary heater) or code 581 (Automatic air conditioning) or code 965 (Taxi/rental car pre-installation) or for hybrid vehicles)

The residual heat utilization function is switched on by pressing the climate control and residual heat ON/OFF menu button (with code 228 (Stationary heater) or code 581 (Automatic air conditioning) or for hybrid vehicles) or the "A/C" and residual heat ON/OFF button (with code 965 (Taxi/rental car pre-installation)) on the air conditioning control panel. The A/C control unit reads in the control signals of the climate control operating unit via climate control LIN and actuates the coolant circulation pump directly. The coolant circulation pump delivers the still warm (residual heat) coolant through the heat exchanger.

The climate control control unit actuates the electronic blower motor via climate control LIN 2 at the same time. The intake air from the electronic blower motor is routed past the heater heat exchanger and heated up in the process. The function is terminated after 30 min or when the on-board electrical system voltage drops below a certain value.

Shutoff of air conditioning after an accident (crash signal sent)

In order to prevent harmful gases entering the vehicle interior after an accident, the climate control control unit starts the following activities:

 The electronic blower motor is no longer actuated. The air is no longer circulated in the vehicle interior.

 The left electronic booster blower and the right electronic booster blower are no longer actuated. The air is no longer circulated in the rear of the vehicle.

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

 The refrigerant compressor regulation valve is switched off (model 213 (except for hybrid vehicles except code B09 (Refrigerant compressor with magnetic clutch))). 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 electric refrigerant compressor is no longer energized (for hybrid vehicles).

 The PTC heater booster is switched off (engine 654, 642 or 274 with code 401 (Seat climate control for driver and front passenger) or code 824 (Additional parts for countries with cold temperatures) or code 873 (Seat heating for driver and front passenger) or code 902 (Seat heating Plus for driver and front passenger) except code 228 (Stationary heater) or code 913 (Hot countries code) or for hybrid vehicles).

 The high voltage PTC heater is switched off (for hybrid vehicles).

The supplemental restraint system control unit transmits the crash signal via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the A/C control unit.

 Detailed information on actuation of the individual components in the air conditioning is available in the "Actuating the A/C components" chapter.