Climate control regulation, function

P83.40-5455-79

Function requirements, general

For regulating the climate control:

 Terminal 15 ON

 Automatic air conditioning switched on

For cooling operation:

 Engine running (engine 177, 264, 654, 656)

 Refrigerant compressor switched on

For evaporator drying process:

 Engine Off

For residual heat utilization (with code 228 (Stationary heater) or code 581 (Automatic air conditioning)):

 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 are carried out depending on the following variables:

 Selected settings on climate control operating unit

 Selected settings on rear climate control operating unit (with code 581 (Automatic air conditioning))

 Selected settings in the head unit

 Various sensor signals (e.g. vehicle interior temperature, outside temperature, coolant temperature, vehicle speed)

The climate control unit is networked with the vehicle electronics via the interior CAN, the front A/C control LIN, A/C control LIN 2 and the A/C operating LIN. 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

 Fresh air mode

 Recirculated air mode

 Defrost

 Evaporator drying

 Residual heat utilization (with code 228 (Stationary heater) or code 581 (Automatic air conditioning))

 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 sunroof (with code 414 (Sliding sunroof))

 Operating settings

 Status of voice control system (VCS [SBS]) (with code 531 (COMAND APS) or code 357 (Map navigation))

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 signals from the vehicle interior temperature sensor directly and sends the vehicle interior temperature over 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 required to control the blend air flaps and to actuate 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. This serves to prevent the evaporator from icing up. As of an evaporator temperature of 2.5 °C, the refrigerant compressor is switched on again.

The evaporator temperature is kept at 2.5 °C for max. 20 min. The evaporator temperature is then adjusted to a range between 3 and 8 °C (depending on the cooling output requirement).

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 bar or > 28 bar the refrigerant compressor is switched off or not activated.

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.

With code 531 (COMAND APS) or code 357 (Map navigation):

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 provides 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 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 unit reads in the signals from the air quality sensor via the front A/C control LIN. 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 sunroof (with code 414 (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.

If the 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

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))

 Right temperature selection button

 Climate control menu button (with code 580 (Air conditioning system) except code 228 (Stationary heater))

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

 "SYNC" button (with code 580 (Air conditioning system) except code 228 (Stationary heater))

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

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

 Blower button, front

 AUTO button, front

 Defrosting button

 Air distribution button (with code 580 (Air conditioning system))

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 and sends a switch-on request to the Audio/COMAND display via telematics CAN. The picture data are sent by the head unit over 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 is installed. If this button is not installed, switching off is conducted through the head unit menu.

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 air conditioning system functions. 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 and sends a switch-on request to the Audio/COMAND display via telematics CAN. The picture data are sent by the head unit over the HSVL line to the Audio/COMAND display.

Status of the VCS (with code 531 (COMAND APS) or code 357 (Map navigation))

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 actuation of the A/C components partial function includes the following subfunctions:

 Actuation of electronic blower motor

 Actuation of air ducting flaps

 Actuation of refrigerant compressor

 Actuation of fan motor (engine fan)

 Actuation of PTC heater booster (engine 264 with code 401 (Seat climate control for driver and front passenger) or code 824 (Additional part 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) and except code 913 (Hot-country code), engine 654 except code 228 (Stationary heater) and except code 913 (Hot-country code), engine 656 except code 228 (Stationary heater) and except code 913 (Hot-country code))

 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 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 257, 290
with code 357 (Map navigation)
Model 257, 290
with code 531 (COMAND APS)
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 air ducting flaps

Adjustment of the air ducting flaps in the air conditioner housing regulates the air distribution in the vehicle interior. The following components are actuated by the climate control unit via the front A/C control LIN:

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)

P83.10-2946-76

Actuation of refrigerant compressor

Engine 177

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.

Engine 264, 654, 656

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.

Engine 256

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.

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 sent), the refrigerant compressor is switched off via the refrigerant compressor regulating valve or via the refrigerant compressor magnetic clutch (engine 177, 264, 654, 656).
In the event of an accident (crash signal sent), the electric refrigerant compressor (engine 256) is switched off.

Actuation of fan motor (engine fan)

The fan motor is used for cooling the coolant and refrigerant. The climate control control unit calculates the specified fan speed depending on the refrigerant pressure and sends this over the interior CAN, electronic ignition lock control unit and the suspension FlexRay to the powertrain control unit.

The powertrain control unit corrects the requested fan speed to match the engine temperature and regulates the fan motor over the drivetrain LIN accordingly.

Actuation of PTC heater booster (engine 264 with code 401 (Seat climate control for driver and front passenger) or code 824 (Additional part 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) and except code 913 (Hot-country code), engine 654 except code 228 (Stationary heater) and except code 913 (Hot-country code), engine 656 except code 228 (Stationary heater) and except code 913 (Hot-country code))

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 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 or when the engine has stopped, the coolant circulation pump is also actuated. This serves to ensure that the flow volume required to heat up the blowby air is adequate. 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.

Shift point adjustment

If cooling or heating requirements increase, the fully integrated transmission control electric controller unit control unit can shift the switch point.

The climate control control unit sends the request to shift the switch point over the interior CAN, electronic ignition lock control unit, the suspension FlexRay, powertrain control unit and the drive CAN to the fully integrated transmission control electric controller unit control unit.

Fresh air mode

The fresh air/ram air/air recirculation flap is open during fresh air mode. Fresh air is routed through the air conditioner housing into the vehicle interior.

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

Recirculated air mode

The air recirculation mode partial function includes 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

By pressing the air recirculation mode button on the climate control operating unit for less than 1.5 s, the fresh air/ram air/air recirculation flap is closed. This prevents any air flow 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 unit actuates the fresh air/ram air/air recirculation flap actuator motor via the front A/C control LIN. It then transmits the status "air recirculation mode active" via the A/C operating LIN to the climate control operating unit. The climate control operating unit 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) and except code 494 (USA version) and except code 835 (Additional parts for South Korea vehicles):

If the air recirculation mode button is pressed for > 1.5 s, the side windows and the sliding sunroof (with code 414 (Sliding sunroof)) are closed. If the air recirculation mode button is pressed for > 1.5 s, the side windows and the sliding sunroof (with code 414 (Sliding sunroof)) are opened again. If the side windows and the sliding sunroof (with code 414 (Sliding sunroof)) are not manually adjusted during the air recirculation mode, they are returned to their default positions.

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 via the front A/C control LIN to the climate 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) or code 357 (Map navigation))

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 climate control unit actuates the fresh air/ram air/air recirculation flap actuator motor via the front A/C control LIN, 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))

Pressing the climate control menu and residual heat ON/OFF button switches on the residual heat utilization function. 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 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 is switched off. The refrigerant compressor no longer circulates the refrigerant.

 The PTC heater booster is switched off (engine 264 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) and except code 913 (Hot-country code), engine 654 except code 228 (Stationary heater) and except code 913 (Hot-country code), engine 656 except code 228 (Stationary heater) and except code 913 (Hot-country code)).

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.