Climate control regulation, function

P83.40-5391-79

Function requirements, general

For regulating the climate control:

 Terminal 15 ON

 Automatic air conditioning switched on

For the cooling mode and defroster function:

 Engine runs

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

For evaporator drying process:

 Engine Off

For residual heat utilization:

 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 via 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 climate control control unit regulates the temperature and the air distribution in the vehicle interior to match the settings made and the variables recorded by the various sensors (e.g. interior temperature, outside temperature, coolant temperature, vehicle speed). Appropriate settings can be made on the climate control operating unit, on the rear A/C system operating unit (model 222 with code 582 (A/C system in rear)) and via the air conditioning menu in the COMAND controller unit or in the head unit.

The climate control control unit is networked to the vehicle electronics over the interior CAN, climate control LIN 1, climate control LIN 2, climate control LIN 3 and climate control LIN. This enables relevant parameters to be incorporated in order to improve regulation quality and to lower energy consumption.

A/C control includes the following partial functions:

 Recording and evaluation of variables

 Actuation of air conditioning components

 Safety shutoff

 Shift point adjustment

 Fresh air mode

 Recirculated air mode

 Defrost

 Evaporator drying

 Residual heat utilization

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

 Temperature on evaporator of front A/C system

 Temperature at evaporator of rear A/C system (model 222 with code 582 (A/C system in rear))

 Temperature at heat exchanger of rear A/C system (model 222 with code 582 (A/C system in rear))

 Refrigerant pressure

 Refrigerant temperature

 Solar radiation

 CO2 concentration level in vehicle interior

 Air quality

 Vehicle speed

 Engine speed

 Door status

 Position of side windows

 Position of panoramic sliding sunroof (model 222 with code 413 (Panoramic sliding sunroof))

 Rate of air flow of air vents

 Operating settings

 Voice control system (VCS) status

Outside temperature

The outside temperature is recorded by the outside temperature sensor. The front SAM control unit directly reads in the outside temperature sensor signals, calculates the outside temperature and sends the data to the climate control control unit via 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 incorporated into the interior temperature regulation, when the vehicle speed is more than 20 km/h. At speeds less than 20 km/h and when the ignition is switched off and on, the last measured temperature value is used.

Interior temperature in head area

The interior temperature in the head area is recorded by the interior temperature sensor in 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 sends this, for vehicles up to model year 2018, via the roof LIN, front SAM control unit and the interior CAN to the climate control control unit. For vehicles from model year 2018, the overhead control panel control unit reads in the value of the interior temperature and sends 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.

Temperature on evaporator of front A/C system

The temperature at the evaporator of the front A/C system is recorded by the evaporator temperature sensor. The A/C control unit reads in the signals from the evaporator temperature sensor directly.

If the temperature at the evaporator drops to below 2 °C, the climate control control unit switches off the refrigerant compressor. This helps to prevent any icing up of the evaporator on the front A/C system. From a temperature at the evaporator of 2.5 °C, the climate control control unit switches on the refrigerant compressor again.

The temperature at the evaporator of the front A/C system is maintained for a maximum of 30 min. at 2 °C. After this, it is regulated (depending on cooling performance requirement) to a range between 3 and 8 °C.

Temperature at evaporator of rear A/C system (model 222 with code 582 (A/C system in rear))

The temperature at the evaporator of the rear A/C system is recorded by the rear A/C system evaporator temperature sensor. The climate control control unit reads in the signals from the rear A/C system evaporator temperature sensor directly.

If the temperature at the evaporator of the rear A/C system drops below 2 °C, the climate control control unit blocks the supply of refrigerant to the evaporator of the rear A/C system through the rear A/C system evaporator CO2 shutoff valve. This helps to prevent any icing up of the evaporator of the rear A/C system. From a temperature at the evaporator of the rear A/C system of 2.5 °C, the climate control control unit opens the supply of refrigerant again.

Temperature at heat exchanger of rear A/C system (model 222 with code 582 (A/C system in rear))

The temperature on the rear A/C system heat exchanger is recorded by the temperature sensors for the rear A/C system heat exchanger. The climate control control unit reads in the signals from the rear A/C system heat exchanger temperature sensors directly, and regulates the temperature accordingly at the air outlets.

Refrigerant pressure

The refrigerant pressure is recorded by the CO2 pressure/temperature sensor upstream of the gas cooler. The climate control control unit directly reads in the signals of the CO2 pressure/temperature sensor upstream of the gas cooler. The pressure is compared with a stored temperature/pressure curve. At a refrigerant pressure of less than 24 or more than 140 bar, the climate control control unit switches off the refrigerant compressor or it does not switch it on.

Refrigerant temperature

The refrigerant temperature upstream of the gas cooler is recorded by the CO2 pressure/temperature sensor upstream of the gas cooler. The refrigerant temperature downstream of the gas cooler is recorded by the CO2 pressure/temperature sensor downstream of the gas cooler. The comparison of both values enables the gas cooler function to be monitored. The climate control control unit directly reads in the signals from the CO2 pressure/temperature sensors.

Solar radiation

The angle of incidence and the intensity of the solar radiation on the vehicle are recorded by the sun sensor and the rear sun sensor.

The climate control control unit directly reads in the signals from the sun sensor. The rear SAM control unit reads in the signals of the rear sun sensor directly and sends this information over the interior CAN to the climate control control unit. In the event of one-sided solar radiation, an appropriate temperature difference is set between the left and the right specified control temperatures.

CO2 concentration level in vehicle interior

The CO2 concentration level in the vehicle interior is recorded by the CO2 sensor at the front air conditioning housing. For model 222 with code 582 (A/C system in rear), there is also a CO2 rear sensor installed at the rear air conditioning housing. This records the concentration of CO2 in the rear compartment.

The CO2 sensors send corresponding information via the climate control LIN 3 to the climate control control unit. To match the CO2 concentration level in the vehicle interior, the climate control control unit supplies fresh air or switches off the A/C system. Appropriate warnings are shown on the instrument cluster.

 Detailed information on the safety strategy is available in the Safety Shutoff chapter.

Air quality

The multifunction sensor records the concentration levels for the following pollutants in the outside air:

 Carbon monoxide (CO)

 Nitrogen oxides (NOx)

The multifunction sensor also records the temperature and humidity level of the outside air and calculates the outside dew point temperature. The multifunction sensor sends the corresponding information over the climate control LIN 2 to the climate control control unit. The climate control control unit uses this to derive the automatic air recirculation. 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 among other things to regulate the refrigerant compressor.

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 (model 222)

 Right rear door control unit (model 222)

When a door is opened, the climate control control unit references the values of the interior temperature sensor 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 (model 222)

 Right rear door control unit (model 222)

 Rear control unit (model 217)

When side windows are opened, the climate control control unit references the values of the interior temperature sensor 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 panoramic sliding sunroof (model 222 with code 413 (Panoramic sliding sunroof))

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.

When the panoramic sliding roof is opened, the climate control control unit references the values of the interior temperature sensor 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.

Rate of air flow of air vents

The rate of air flow at the air vents and therefore the ventilation intensity can be adjusted by turning the following components:

 Left side air vent potentiometer

 Right side air vent potentiometer

 Left center air vent potentiometer

 Right center air vent potentiometer

 Left rear center air vent potentiometer

 Right rear center air vent potentiometer (model 222 with code 582 (A/C system in rear))

The climate control control unit reads in the signals of the potentiometers directly.

Operating settings

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

 Climate control operating unit

 Rear A/C system operating unit (model 222 with code 582 (A/C system in rear))

 COMAND controller unit or head unit

Climate control operating unit

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

 Left AUTO button

 Left temperature selection button

 Left blower button

 Air recirculation mode button

 Climate control menu and residual heat ON/OFF button (model 217.3, 222 with code 228 (Stationary heater))

 Rear window heater button

 Stationary heater button (model 217.3, 222 with code 228 (Stationary heater))

 Right blower button

 Right temperature selection button

 Right AUTO button

 Climate control menu button (except CODE 228 (Stationary heater))

 Residual heat ON/OFF button (except CODE 228 (Stationary heater))

 Defrosting button

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. The climate control control unit sends corresponding information for this via the interior CAN, electronic ignition lock control unit and the user interface CAN to the COMAND controller unit or the head unit. The COMAND controller unit or the head unit generates the corresponding image data, transmits a switch-on request to the Audio/COMAND display via the telematics CAN and transfers the image data to the Audio/COMAND display via the LVDS or HSVL line. 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 only be switched off using the air conditioning menu.

 The setting for the front air distribution can only be made using the air conditioning menu and appears on the Audio/COMAND display.

Rear A/C system operating unit (model 222 with code 582 (A/C system in rear))

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 flow, air distribution and interior temperature in the rear. The settings are shown in the display of the rear air conditioning operating unit.

 The rear A/C system can also be operated using the climate control operating unit or via the air conditioning menu. The A/C system in the rear can then not be operated using the rear A/C system operating unit.

COMAND controller unit or head unit

The A/C system can be switched off or the climate control functions selected using the air conditioning menu in the COMAND controller unit or the head unit. The COMAND controller unit or the head unit sends the corresponding information via the CAN user interface, electronic ignition lock control unit and interior CAN to the climate control control unit, generates the corresponding image data, sends a switch-on request via the telematics CAN to the Audio/COMAND display and transfers the image data to the audio/COMAND display via the LVDS or HSVL line.

VCS status

When the VCS is active, the climate control control unit reduces the output of the blower motor using the blower regulator. The COMAND controller unit or the head unit transmits the status of the VCS via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the A/C control unit.

Actuation of air conditioning components

Actuation of the air conditioning components encompasses the following subfunctions:

 Actuation of blower motor

 Actuation of rear blower motor (model 222 with code 582 (A/C system in rear))

 Actuation of air ducting flaps

 Actuation of refrigerant compressor

 Actuation of CO2 expansion valve or CO2 expansion valve for rear air conditioning system (model 222 with code 582 (air conditioning system in rear))

 Actuation of fan motor

 Actuation of PTC heater booster (model 222 with diesel engine)

 Actuation of coolant circulation pump

 Actuation of rear heating system valve unit (model 222 with code 582 (A/C system in rear))

 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 A/C system water valve

Actuation of blower motor

Ventilation of the vehicle interior is achieved with the aid of the blower motor. The climate control control unit sends the corresponding request over the climate control LIN 2 to the blower regulator, 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 keeps the windows free of any fogging and supplies the vehicle occupants with air. 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.

 With VCS [SBS] active, the blower setting is reduced.

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

Actuation of rear blower motor (model 222 with code 582 (A/C system in rear))

The rear blower motor is used for ventilation of the rear. The climate control control unit actuates the rear blower motor over the climate control LIN 2.

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

Actuation of air ducting flaps

Adjusting the air ducting flaps regulates the air distribution in the vehicle interior.

The following air ducting flaps are adjusted:

 Air recirculation flap via the air recirculation flap actuator motor (air recirculation control)

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

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

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

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

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

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

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

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

 Upper left blend air flap via the upper left blend air flap actuator motor (temperature control)

 Lower left blend air flap via the lower left blend air flap actuator motor (temperature control)

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

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

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

 Left A-pillar air distribution flap over left A-pillar air distribution actuator motor (ventilation control)

 Right A-pillar air distribution flap over right A-pillar air distribution actuator motor (ventilation control)

 Left B-pillar air distribution flap over the left B-pillar air distribution actuator motor (model 222) (ventilation control)

 Right B-pillar air distribution flap over the right B-pillar air distribution actuator motor (model 222) (ventilation control)

 Left rear center air vent flap over the left rear center air vent actuator motor (model 222) (ventilation control)

 Right rear center air vent flap over the right rear center air vent actuator motor (model 222 with code 582 (Rear A/C system) (ventilation control)

The A/C control unit actuates the actuator motors over the climate control LIN 1.

 The recirculated air flap is closed in the event of an accident (crash signal sent).

 To prevent any fogging of the windows, 2 minutes after switching off circuit 15, the defroster flaps are closed and the footwell flaps are opened. After starting the engine all the settings are available again.

 At terminal 15 OFF, when one of the doors is opened, the air recirculation flap is set by the air recirculation flap actuator motor to an opening angle of 50 %. The door closing forces are thereby reduced. The function can be set with the diagnostic tester.

P83.10-2829-76

Actuation of refrigerant compressor

The refrigerant compressor is responsible for induction and compression of the refrigerant.

A magnetic clutch is integrated into the refrigerant compressor's belt pulley. This magnetic clutch can be used to disconnect the refrigerant compressor completely from the power flow in the belt drive. This in turn enables additional fuel savings to be made. The climate control control unit directly regulates the refrigerant compressor magnetic clutch.

The output of the refrigerant compressor is continuously regulated by the climate control control unit up to 100 %. The A/C system control unit actuates the refrigerant compressor regulating valve directly.

Apart from this, 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 drive-train 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 on under the following conditions:

 Refrigerant pressure over 26 bar

 Refrigerant pressure below 93 bar

 Refrigerant temperature upstream of gas cooler under 160 °C

The refrigerant compressor is not switched on or switched off under the following conditions:

 Refrigerant pressure below 24 bar (switch-on interlock for lack of refrigerant)

 Refrigerant pressure over 95 bar (switch-on interlock when static pressure too high)

 Refrigerant pressure over 140 bar (shutoff at overpressure)

 Refrigerant temperature upstream of gas cooler over 170 °C (shutoff at overtemperature)

 As from a refrigerant pressure of 133 bar or a refrigerant temperature of 165 °C, the output of the refrigerant compressor is governed by the actuator current.
In the event of an accident (crash-signal sent), the refrigerant compressor is switched off and disconnected by the refrigerant compressor magnetic clutch from the belt drive.

Actuation of CO2 expansion valve or CO2 expansion valve for rear air conditioning system (model 222 with code 582 (air conditioning system in rear))

The CO2 expansion valve restricts the flow of refrigerant and releases it into the front air conditioning evaporator in a targeted manner.

The CO2 expansion valve in the rear air conditioning system restricts the flow of refrigerant and releases it into the rear air conditioning evaporator in a targeted manner.

The climate control control unit actuates the CO2 expansion valves via the climate control LIN 3. The opening angle of the CO2 expansion valves can thereby be continuously adjusted between 13 and 100 %.

Actuation of fan motor

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 temperature 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 (model 222 with diesel engine)

When required, the PTC heater booster is switched on by the climate control control unit over the climate control LIN 1. 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 coolant circulation pump

Driven by the coolant pump, the coolant circulates in the engine cooling circuit. In the process, it absorbs engine heat. The heated coolant passes through the heater heat exchanger, which dissipates heat to the air blowing by and thus heats the vehicle interior.

At low engine speed and with an engine stop in ECO start-stop mode, the coolant circulation pump is also actuated to ensure that the flow rate required for heating the vehicle interior is sufficient. The coolant circulation pump is actuated directly by the A/C system control unit.

Actuation of rear heating system valve unit (model 222 with code 582 (A/C system in rear))

The rear heating system valve unit consists of the left Duo valve and the right Duo valve. The valves are used to control the supply of coolant to the rear heat exchanger. The climate control control unit directly actuates the rear heating system valve unit.

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

 Ionization activated

 Blower switched on

 Left side air vent flap opened

 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-up. The ionization of the interior air itself is odor-neutral and cannot be detected directly as such in the vehicle.

The ionization is switched on and off via the air conditioning menu. The COMAND controller unit or the head unit sends the “Switch on ionization” request via the user interface CAN, electronic ignition lock control unit and interior CAN to the A/C 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 alternator is used to supply fragrance to the vehicle interior. A fan is installed in the fragrance generator, which produces a flow of 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). 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 perfume atomizer is switched on and off using the A/C menu in the COMAND controller unit or the head unit. The intensity can be adjusted in three stages. The COMAND controller unit or the head unit sends the “Switch on perfume atomization” request and the “Perfume atomization intensity” request 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 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. Additionally, the perfume atomizer generator switches off the flask illumination and the perfume atomization intensity last set in the climate control menu is activated.

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 A/C system water valve

The air conditioning water valve controls the supply of coolant to the heat exchanger of the air conditioning housing. In order to achieve efficient cooling by the evaporator, the air conditioning system water valve is closed and therefore the flow of warm coolant through the heat exchanger is interrupted. The climate control control unit actuates the air conditioning water valve directly.

Safety shutoff

To enable appropriate measures to be initiated in the event of any leakage in the refrigerant circuit early on, the CO2 concentration level in the vehicle interior is continuously monitored. The CO2 refrigerant is denser than air and drops to the floor in the event of any leakage. The health hazard effect of CO2 therefore lies in the displacement of oxygen. If a leakage is detected, the climate control control unit starts the active ventilation of the vehicle interior (active scavenging process). Different warnings are also shown on the instrument cluster. To this end, the climate control control unit sends the corresponding request over the interior CAN, electronic ignition lock control unit and the user interface CAN to the instrument cluster.

 At a CO2 concentration level of more than 5,000 ppm when driving, the climate control control unit starts the fresh air mode or partial air recirculation mode function (where air recirculation mode was previously in use).

The air recirculation mode is not enabled again until the CO2 concentration level of 5,000 ppm is undershot.

 At a CO2 concentration level of more than 10,000 ppm when driving, the climate control control unit starts active ventilation.

The climate control control unit activates the fresh air mode, blower setting 2 and the footwell air distribution.

These measures are only canceled once the CO2 concentration level drops to less than 5,000 ppm.

 At a CO2 concentration level of more than 25,000 ppm when driving, the climate control control unit starts active ventilation.

The climate control control unit activates the fresh air mode, blower setting 2 and the footwell air distribution. Furthermore, the warning “Air conditioning fault, see Owner's Manual” will appear in the instrument cluster and a warning tone is emitted. These measures are only canceled once the CO2 concentration level drops to less than 5,000 ppm.

 At a CO2 concentration level of more than 25,000 ppm over a time period of 5 minutes when driving, the climate control control unit starts the active ventilation process.

The climate control control unit activates the fresh air mode, at least blower setting 2 and the footwell air distribution. The "Malfunction, supply vehicle interior with fresh air, Service Required" warning is also shown in red in the instrument cluster and a warning tone emitted. These measures are only canceled once the CO2 concentration level drops to less than 25,000 ppm.

 At a CO2 concentration level of more than 25,000 ppm while parking, the climate control control unit is woken up.

The climate control control unit starts the active ventilation and activates the fresh air mode, blower setting 2 and the footwell air distribution. The "Malfunction, supply vehicle interior with fresh air, Service Required" warning is also shown in red in the instrument cluster and a double warning tone emitted. The double warning tone is repeated 60-times.

These measures are only canceled once the CO2 concentration level drops to less than 5,000 ppm.

 When the accuracy of the sensors is reduced, the climate control control unit starts active ventilation.

The climate control control unit activates the fresh air mode, blower setting 2 and the footwell air distribution. Furthermore, the warning “Air conditioning fault, see Owner's Manual” will appear in the instrument cluster and a warning tone is emitted. These measures are not automatically canceled and they are shown at each restart.

 If the CO2 sensor fails, the climate control control unit starts the active ventilation.

The climate control control unit activates the fresh air mode, blower setting 2 and the footwell air distribution. When driving, the "Malfunction, supply vehicle interior with fresh air, Service Required" warning is also shown in red in the instrument cluster and a double warning tone emitted. If the vehicle is parked, the "Malfunction, supply vehicle interior with fresh air, Service Required" warning is shown in red in the instrument cluster and a double warning is emitted that is repeated 60-times.

The message remains visible in the instrument cluster until the malfunction is rectified.

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

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

 The rear blower motor (model 222 with code 582 (A/C system in rear)) is no longer actuated. The air is no longer circulated in the rear compartment.

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

 The output of the refrigerant compressor is reduced by the refrigerant compressor regulating valve. The refrigerant compressor magnetic clutch is opened. The belt pulley of the refrigerant compressor is no longer driven.

 The PTC heater booster (model 222 with diesel engine) is switched off.

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 individual components in the air conditioning is available in the "Actuating the A/C components" chapter.

Shift point adjustment

If the cooling or heating requirement increases, the fully integrated transmission control unit can be used to 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 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 flap actuator motor over the climate control LIN 1.

Recirculated air mode

Air recirculation mode encompasses the following subfunctions:

 Air recirculation mode via the air recirculation mode button

 Pollutant-controlled air recirculation mode

Air recirculation mode via the air recirculation mode button

Operating the air recirculation mode button on the climate control operating unit for more than 1.5 s, the air recirculation flap and the side windows and panoramic sliding sunroof (model 222 with code 413 (Panoramic sliding sunroof)) are also closed to prevent any outside air entering. 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 sends the status of the air recirculation mode button via the climate control LIN to the climate control control unit. The climate control control unit then actuates the fresh/recirculated air flap actuator motor via the air-conditioning control LIN 1.

If the air recirculation mode button is then pressed for longer than 1.5s, the side windows, the panoramic sliding sunroof (model 222 with code 413 (Panoramic sliding sunroof)) and the air recirculation flap are moved back to the default position (insofar as they were not manually adjusted during the air recirculation mode).

Additional function requirements for pollutant- controlled air recirculation mode

 Cooling operation active

Pollutant-controlled air recirculation mode

The multifunction sensor transmits the outside air pollutant values via climate control LIN 2 to the A/C control unit. Starting from a certain pollutant concentration, the 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, then fresh air is initially supplied for 30 s. After this, operation continues with 80 % of the pollutant-sensitive air recirculation mode and after another 10 s, as required, 100 % of the pollutant-sensitive air recirculation mode.

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

Defrost

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. 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 operating unit sends the status of the defrosting button via the climate control LIN to the climate control control unit. The climate control control unit actuates the blower regulator via the climate control LIN 2 and this actuates the blower motor so that an optimum defrost mode is ensured to match the vent air temperature.

The refrigerant compressor is switched in to ensure that the vent air is dried. The air is dried and then heated up to the maximum temperature.

Additional function requirements for evaporator drying process

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

 Evaporator temperature above 3 °C

 Outside temperature above 20°C

 Doors closed

 Kilometer reading over 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 transmits 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 via 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 control unit, which starts the evaporator drying process. For a period of 30 minutes, the blower motor and rear blower motor (model 222 with code 582 (A/C system in rear)) are actuated at the lowest blower setting.

The climate-control control unit sends the corresponding request over the climate control LIN 2 to the blower regulator, which actuates the blower motor.

In model 222 with code 582 (A/C system in rear), the climate control control unit actuates the rear blower motor over the climate control LIN 2.

The air supply serves to reduce residual moisture in the evaporator in both instances.

Residual heat utilization

Operation of the residual heat ON/OFF button on the climate control operating unit switches on the residual heat utilization function.

The climate control operating unit sends the status of the residual heat ON/OFF button over the climate control LIN to the climate control control unit. The climate control control unit then actuates the coolant circulation pump. This routes the warm coolant (residual heat) through the heater heat exchanger.

At the same time, the climate control control unit sends the ventilate request via the climate control LIN 2 to the blower regulator, which then actuates the blower setting at the lowest stage. The intake air is routed past the heater heat exchanger which heats it up. The function is terminated after 30 minutes or when the on-board electrical system voltage drops below a certain value.