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Home >> Mercedes Benz >> 2015 >> C400 >> Repair and Diagnosis >> Heating, Ventilation & A/C (HVAC) >> HVAC Control Systems >> Climate Control - 205 Chassis (4D Sedan) >> Basic Knowledge >> Climate control regulation, function - GF83.40-P-2012RF

Climate control regulation, function - GF83.40-P-2012RF

Model 205, 253 

Fig 1: Climate Control Regulation Block Diagram (1 Of 2)
G10134831Courtesy of MERCEDES-BENZ USA
Fig 2: Climate Control Regulation Block Diagram (2 Of 2)
G10134832Courtesy of MERCEDES-BENZ USA

IMPORTANT Model 205.012/047/147/212/247

The battery management system control unit is integrated in the high-voltage battery module (A100).

Function requirements, general 

For regulating the climate control:

For cooling operation:

For evaporator drying process:

For residual heat utilization (with code 228 (Stationary heater) or code 581 (Automatic air conditioning) or code 965 (Taxi/rental car preinstallation) or model 205.047/147/247):

IMPORTANT The electronic ignition lock control unit sends the status of circuit 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 unit.

Climate control, general 

The electronic temperature control and the air distribution in the vehicle interior are carried out depending on the settings selected at the front climate control operating unit, the rear climate control operating unit (with CODE 581 (Automatic air conditioning)) or the Audio/COMAND control panel and the variables (e.g. interior temperature, outside temperature, coolant temperature and vehicle speed) recorded by various sensors. Determination of these variables is described below.

IMPORTANT Detailed information on possible settings is available in the separate component description for the "Front climate control operating unit".

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:

Function sequence for recording and evaluating variables 

The following variables are recorded and evaluated:

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 A/C control unit requires this value to achieve the required interior temperature by adjusting the blend air flaps accordingly.

IMPORTANT If the vehicle is stationary, the measured temperature can differ considerably from the outside temperature. This is why the outside temperature is only taken account for the regulation, if the vehicle speed was more than v = 30 km/h for a period of at least t = 30 s. At speeds of v < 30 km/h as well as when switching the ignition on and off, the temperature value measured last is 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 sucks in the air for temperature measurement from the vehicle interior. The front SAM control unit reads in the value of the interior temperature via roof LIN and transmits this via 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 of the air outlet temperature sensors are read in directly by the A/C control unit. The climate-control control unit regulates the air outlet temperature at each of the air outlets.

Temperature and moisture on windshield 

The humidity and temperature sensor integrated in the rain/light sensor with additional functions measures the relative humidity and temperature directly on the inside of the windshield and uses this to determine the dew point temperature. The surface temperature on the windshield is also determined. The comparison with the dew point temperature enables any (impending) fogging of the windshield to be detected. The temperature values of the rain/light sensor with additional functions are read in by the front SAM control unit via the rain/light sensor LIN. The front SAM control unit sends the signals over the interior CAN to the A/C control unit. If the windshield threatens to fog up, corresponding countermeasures are taken such as, e.g. switching on the refrigerant compressor or starting the engine.

Coolant temperature 

The coolant temperature is recorded by the coolant temperature sensor. The CDI control unit or the ME-SFI [ME] control unit reads in the signals of the coolant temperature sensor directly and transmits information about the coolant temperature via the drive train CAN, the powertrain control unit, the chassis FlexRay, the electronic ignition lock control unit and the interior CAN to the climate control unit. The value is used to control the blend air flaps and to actuate the coolant circulation pump.

On model 205.047/147/247, the coolant temperature in the high-voltage PTC heater is also recorded by the high-voltage PTC heater temperature sensor. The climate 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 actuate the heater circuit circulation pump.

Temperature on evaporator 

To prevent the evaporator from icing up, the temperature there is recorded by the evaporator temperature sensor. The climate control unit reads in the signals from the evaporator temperature sensor directly. If the evaporator temperature drops to approx. T = 2 °C, the refrigerant compressor is switched off or the front evaporator shutoff valve (model 205.012/047/147/212/247) is closed. As of a temperature of T = 2.5 °C, the refrigerant compressor is switched on again or the front evaporator shutoff valve (model 205.012/047/147/212/247) is opened again.

Temperature T = 2.5 °C is maintained for a maximum of t = 20 minutes after switching on the ignition. The temperature is then regulated to a range between T = 3 °C and T = 8 °C (to match the required cooling output).

Refrigerant pressure 

The refrigerant pressure is recorded by the refrigerant pressure sensor. The signals for the refrigerant pressure sensor are read in directly by the A/C control unit. The pressure is compared with a stored temperature/pressure curve. At a refrigerant pressure of p < 0.8 bar or p > 28 bar, the refrigerant compressor or electric refrigerant compressor is switched off or not activated.

Solar radiation 

The sun sensor integrated in the rain/light sensor with additional functions records the angle of incidence and the intensity of the solar radiation. The signals of the rain/light sensor with additional functions are read in by the front SAM control unit via the rain/light sensor LIN. The front SAM control unit sends the signals over the interior CAN to the A/C control unit. 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.

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

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

The values are read in by the climate-control control unit over the climate control LIN 1. The A/C control unit realizes the automatic air recirculation according to the read-in values.

Vehicle speed 

The vehicle speed is sent by the instrument cluster over the user interface CAN, electronic ignition lock control unit and over the interior CAN to the A/C 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 RPM is sent by the CDI control unit or the ME-SFI [ME] control unit over the drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and the interior CAN to the climate control unit. The engine speed is used among others to regulate the refrigerant compressor.

Door status 

The status of each door is determined by the following control units and sent over the interior CAN to the A/C control unit:

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

Side window position 

The status of each side window position is determined by the following control units and transmitted via interior CAN to the climate control unit:

The climate control unit retains the current blower output when the side windows are opened in order to prevent unnecessary readjustment in the event of high temperature differences between the inside and outside air.

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 climate control unit via the interior CAN. The position of the panoramic sliding sunroof is sent by the panoramic sliding sunroof control unit to the climate control unit via interior CAN.

The climate control unit retains the current blower output when the sliding roof or the panoramic sliding sunroof is open in order to prevent unnecessary readjustment in the event of high temperature differences between the inside and outside air.

Settings on front climate control operating unit 

The A/C settings for the driver and front passenger areas can be adjusted using the following buttons on the front climate control operating unit:

The settings are sent by the front climate control operating unit over the climate control LIN to the climate-control control unit where they are processed. The data are used to regulate the air volume, air distribution and temperature. The selected settings are displayed on the Audio/COMAND display. The climate-control control unit sends the selected settings via interior CAN, electronic ignition lock control unit and 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 image data is sent via the LVDS line to the Audio/COMAND display.

IMPORTANT The air conditioning system or the refrigerant compressor can be switched off if the "A/C" button 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.

IMPORTANT The possible settings for the front air distribution can additionally be made via the Audio/COMAND control panel, and they appear on the Audio/COMAND display.

IMPORTANT Model 205, 253

with code 580 (Air-conditioning system)

The synchronization function can be switched on or off using the "SYNC" button or via the menu in the head unit. The temperature settings on the driver side are also used on the passenger side.

IMPORTANT Model 205, 253

with code 228 (Auxiliary heater)

with code 580 (Air-conditioning system)

The synchronization function can be switched on or off using the menu in the head unit. The temperature settings on the driver side are also used on the passenger side.

IMPORTANT Model 205, 253

with code 581 (Automatic air conditioning)

The synchronization function can be switched on or off using the menu in the head unit. The temperature settings on the driver side are also used on the passenger side and the rear area. Additionally, the front air distribution settings are used for the rear area.

IMPORTANT For feedback on the function, the climate-control control unit sends the request for LED actuation over the climate control LIN to the front climate control operating unit.

Settings on rear climate control operating unit (with CODE 581 (Automatic air conditioning)) 

The climate control function of the rear can be adjusted at the rear climate control operating unit. The settings are transmitted by the rear climate control operating unit via the climate control LIN to the A/C control unit, where they are processed. This information is used to regulate the air volume and the temperature in the rear. The selected settings are shown on the display of the rear climate control operating unit.

Settings on head unit 

The air conditioning system can be switched off or the air conditioning functions selected using the menu in the head unit. The Audio/COMAND operating unit is used to operate it. The control signals are read in and evaluated by the head unit via the telematics CAN. The head unit then transmits the relevant signals via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the climate 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 image data is sent via the LVDS line to the Audio/COMAND display.

Status of VCS [SBS] (with CODE 531 (COMAND APS)) 

If the VCS [SBS] is active, the blower motor output is restricted by the blower regulator. 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 climate-control control unit.

Function sequence for AC component actuation 

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

Function sequence for actuation of blower motor 

Ventilation is achieved with the aid of the blower motor. The climate-control control unit sends the request over the climate control LIN 2 to the blower regulator, which then actuates the blower motor.

IMPORTANT The blower motor drives a radial blower which circulates the air in the vehicle interior or which supplies fresh air to the vehicle interior. This prevents the windows from fogging up, supplies air to the vehicle occupants and allows pleasant and constant temperatures to be reached quickly in the vehicle interior. Depending on the current settings at front climate control operating unit, the air is distributed via various air ducts and air outlets in the vehicle interior.

IMPORTANT Model 205, 253

with code 531 (COMAND APS)

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

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

Function sequence for actuation of electronic blower regulator booster blower (with CODE 581 (Automatic air conditioning)) 

The booster blower electronic blower regulator improves the ventilation in the rear compartment. In order to provide a supply of fresh air from the front to the booster blower electronic blower regulator, the climate control unit transmits the request to actuate the blower motor over climate control LIN 2 to the blower regulator, which actuates the blower motor directly. The level of blower motor actuation depends on the setting on the rear climate control operating unit. The air flow that now arrives in the rear is boosted by the booster blower electronic blower regulator. The climate control unit transmits the request via climate control LIN 2 to the booster blower electronic blower regulator, which boosts the air flow depending on the requested blower setting.

IMPORTANT If the booster blower electronic blower regulator is active, the blower motor is always active as well.

IMPORTANT The booster blower electronic blower regulator is switched off in the event of an accident (crash signal transmitted).

Function sequence for 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 climate control unit via climate control LIN 1:

Vehicles with code 579 (Single-zone air conditioning) or with code 580 (Air conditioning):

IMPORTANT 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 microswitch directly. If an incorrect position is detected, the position of the defroster/footwell/center air vent flap is readjusted by the climate control unit via the defroster/footwell/center air vent flap actuator motor.

Vehicles with CODE 581 (Automatic air conditioning):

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

IMPORTANT The fresh air/recirculated air flap is closed after an accident (crash signal sent).

IMPORTANT Model 205, 253

with code 581 (Automatic air conditioning)

In order to prevent fogging of windows, t = 2 min after switching off terminal 15 the defroster flaps are closed and the footwell flaps are opened. After starting the engine all the settings are available again.

IMPORTANT With circuit 15 Off, the fresh air/ram air/air recirculation flap is moved to an opening angle of 50% by the fresh air/ram air/air recirculation flap actuator motor when one of the doors is opened. The door closing forces are thereby reduced. The function can be set with the diagnostic tester.

Air outlets in the cockpit and in the center console 

Fig 3: Center Console Airflow Diagram
G10134833Courtesy of MERCEDES-BENZ USA

Function sequence for actuation of refrigerant compressor (except model 205.012/047/147/212/247) 

The refrigerant compressor is responsible for induction and compression of the refrigerant. Power for the refrigerant compressor is continuously regulated up to 100% by the climate-control control unit via the refrigerant compressor control valve. The climate-control control unit actuates the refrigerant compressor regulating valve directly.

With CODE B09 (Refrigerant compressor with magnetic clutch), a magnetic clutch is also installed. This can be used to completely disconnect the refrigerant compressor from the belt drive power flow. This in turn enables additional fuel savings to be made. The climate-control control unit directly actuates the refrigerant compressor with magnetic clutch.

The climate control unit also sends the request for an idle speed increase over the interior CAN, electronic ignition lock control unit, chassis FlexRay, powertrain control unit and the drive train CAN to the CDI control unit or the ME-SFI [ME] control unit. This increases the idle speed in accordance with the additional load that occurs when the refrigerant compressor is switched on.

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

Function sequence for actuation of electric refrigerant compressor (model 205.012/047/147/212/247) 

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.

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

IMPORTANT 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.

Function sequence for actuation of fan motor (engine fan) 

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

The CDI control unit or the ME-SFI [ME] control unit then calculates the target blower speed as a function of the engine temperature and actuates the fan motor accordingly.

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

When required, the PTC heater booster is switched on by the climate-control control unit over the climate control LIN 2.

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

Function sequence for actuation of high voltage PTC heater (model 205.047/147/247) 

When required, the high voltage PTC heater is switched on by the climate control unit over the climate control LIN 2. To protect the high voltage PTC heater against damage, it is switched off at a water temperature of T = 90 °C. The water temperature is recorded by the high voltage PTC heater temperature sensor, and read in by the climate control unit over the climate control LIN 2.

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

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

Function sequence for actuation of switchover valve for high voltage PTC heater (model 205.047/147/247) 

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 request to actuate the high voltage PTC heater switchover valve comes from the climate control unit over the climate control LIN 2. The high voltage PTC heater actuates the high-voltage PTC heater switchover valve directly.

Function sequence for actuation of front evaporator shutoff valve (model 205.012/047/147/212/247) 

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

The front evaporator shutoff valve is used to control the flow of refrigerant to the evaporator. Actuation depends on the cooling request.

Function sequence for actuation of coolant circulation pump 

The coolant circulation pump is used to deliver the coolant through the heater heat exchanger. In the process, the coolant absorbs the engine heat. The heated coolant passes through the heater heat exchanger, which dissipates heat to the air blowing by.

Additionally, at low engine RPM, the coolant circulation pump is actuated to ensure that the flow volume needed to heat up the air flowing past is adequate. The coolant circulation pump is actuated directly by the climate-control control unit. Actuation also occurs when the engine is stopped or in electric mode (model 205.012/047/147/212/247).

Function sequence for actuation of heater circuit circulation pump (model 205.047/147/247) 

The heater circuit circulation pump delivers the coolant from the high-voltage PTC heater to the heater heat exchanger, and therefore makes it possible to heat the vehicle interior. The heater circuit circulation pump is directly actuated by the high voltage PTC heater, the request comes from the climate control unit over the climate control LIN 2.

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

Function sequence for 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 ionization cleans and freshens the interior air 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.

IMPORTANT Model 205 (except 205.012/047/147/212/247)

with code 577 (Remote activation of heating and ventilation systems)

Model 205.012/047/147/212/247

The side air vent ionizer at the driver side can also be switched on and off using the pre-entry climate control function.

IMPORTANT The ionization function can only be started via the control menu in the head unit.

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

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

IMPORTANT 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.

Function sequence for 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 and creates its own, clean air flow. When the flask 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. The perfume atomization is pulsed, i.e. it is active for 5 minutes after activation and then switches itself off for 5 minutes. The interval switching is used to prevent the 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 climate-control 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 flask to be used is moved to the working position by the perfume atomizer generator with circuit 15 on. Additionally, the perfume atomizer generator switches off the flask illumination and the perfume atomization intensity set last in the climate control menu of the head unit is activated.

IMPORTANT Model 205 (except 205.012/047/147/212/247)

with code 577 (Remote activation of heating and ventilation systems)

Model 205.012/047/147/212/247

The perfume atomizer generator can also be switched on and off using the pre-entry climate control function.

IMPORTANT The perfume atomization function can only be activated via the control menu in the head unit. The intensity can be adjusted in three stages.

IMPORTANT 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.

Function sequence for actuation of high-voltage battery cooling system shutoff valve (model 205.012/212) 

The high voltage battery cooling system shutoff valve is used to control the flow of refrigerant into the evaporator integrated in the high-voltage battery. This removes thermal energy from the high-voltage battery and prevents any overheating. The battery management system control unit sends the corresponding request over the hybrid CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and the interior CAN to the climate-control control unit.

The A/C control unit sends feedback the opposite way to the battery management system control unit. The high-voltage battery cooling system shutoff valve is directly actuated by the battery management system control unit.

Function sequence for actuation of high-voltage battery cooling system expansion valve (model 205.047/147/247) 

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 over the chassis FlexRay, electronic ignition lock control unit and over the interior CAN to the climate control unit.

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

Function sequence for shift point adjustment (transmission 722.9 (except 722.930), 725 and except model 205.047/012/147/212/247) 

If the cooling or heating requirement increases, the fully integrated transmission control unit can be used to make a shift point adjustment.

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 function sequence 

The fresh air/ram air/air recirculation flap is opened and fresh air is delivered into the vehicle interior through the air conditioner housing.

Air recirculation mode function sequence 

The air recirculation mode function sequence includes the following subfunctions:

Function sequence for air recirculation mode using air recirculation mode button 

Pressing the air recirculation mode button on the front climate control operating unit for t < 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 unit reads in the status of the air recirculation mode button over the climate control LIN and actuates the fresh air/ram air/air recirculation flap actuator motor over the climate control LIN 1.

Vehicles without CODE 494 (USA version):

If the air recirculation mode button is pressed for t > 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 closed. If the air recirculation mode button is then pressed for t > 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 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)) 

Function sequence for pollutant-sensitive 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 climate-control control unit. From a certain pollutant concentration, the climate 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. Outside air supply is prevented and only the inside air is recirculated. If the conditions for the pollutant-controlled air recirculation mode exist after the engine is started, a supply of fresh air is first provided for t = 30 s. After that, operation continues with 80% pollutant-controlled air recirculation mode and then after t = 10 s, as required, with 100% pollutant-controlled air recirculation mode.

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

IMPORTANT The pollutant-controlled air recirculation mode is active for a maximum of t = 30 min.

Additional function requirements for automatic air recirculation mode 

Function sequence for automatic air recirculation mode 

The air recirculation mode is switched on automatically:

The climate 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.

IMPORTANT The automatic air recirculation mode is not shown via the LED of the air recirculation mode button.

IMPORTANT The automatic air recirculation mode is active for a maximum of t = 30 min.

Function sequence for defroster function 

Operating the defrosting button causes all the air flaps with the exception of the defroster flaps 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 A/C control unit actuates the blower regulator over the A/C control LIN 2, and this actuates the blower motor so that optimum defrost mode is guaranteed depending on the exhaust 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 

Function sequence for evaporator drying process 

To counteract evaporator odors in the vehicle interior and fogging of windows when starting the air conditioning, an evaporator drying process is performed.

A timer is activated in the instrument cluster when the engine is switched off. 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 user interface CAN to the instrument cluster.

After a waiting time of t = 1 h, the instrument cluster sends the request for evaporator drying over the user interface CAN, electronic ignition lock control unit and the interior CAN to the A/C control unit, which starts the evaporator drying process. For this purpose, the blower is actuated at the slowest speed for t = 30 min.

The A/C control unit sends the request over the A/C control LIN 2 to the blower regulator. The blower regulator actuates the blower motor at the slowest speed. The air supply serves to reduce residual moisture in the evaporator.

Function sequence for residual heat utilization (with code 228 (Stationary heater) or code 581 (Automatic air conditioning) or code 965 (Taxi/rental car preinstallation) or model 205.047/147/247) 

Pressing the climate control and residual heat ON/OFF menu button (with code 228 (Stationary heater) or code 581 (Automatic air conditioning) or model 205.047/147/247) or the "A/C" and residual heat ON/OFF button (with code 965 (Taxi/rental car preinstallation)) on the front climate control operating unit switches the function on. The climate-control control unit reads in the control signals of the front 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.

Parallel to this, the A/C control unit transmits the ventilate request via A/C control LIN 2 to the blower regulator, which then actuates the blower motor at the lowest setting. The intake air from the blower motor is routed past the heater heat exchanger and heated up in the process. The function is terminated after a time of t = 30 min. has elapsed or when the on-board electrical system voltage drops below a certain value.

Function sequence for shutoff of air conditioning after an accident (crash signal sent) 

In order to prevent the ingress of harmful gases into the vehicle interior after an accident, the A/C control unit starts the following activities:

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.

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

  Electrical function schematic for climate control input signals   PE83.40-P-2056-97FBA 
  Electrical function schematic for climate control actuation   PE83.40-P-2057-97FBA 
  Overview of system components for climate control   GF83.40-P-9994RF 
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