LEMON Manuals: Even more car manuals for everyone
Home >> Mercedes Benz >> 2019 >> C300 4Matic, 2D Convertible >> Repair and Diagnosis >> External Pages >> Different car >> Section 327 (Climate Control - 253 Chassis 1 Of 3) >> Basic Knowledge >> Climate Control Regulation, Function - GF83.40-P-2012RF

Climate Control Regulation, Function - GF83.40-P-2012RF

WARNING: This page is about a different car, the 2023 Mercedes-Benz GLC300, 2022 Mercedes-Benz GLC300, 2021 Mercedes-Benz GLC300, 2020 Mercedes-Benz GLC350e, and 2020 Mercedes-Benz GLC300. However, it is still accessible from the selected car via links, so may be relevant.

Model 205, 253 

G14188741Courtesy of MERCEDES-BENZ USA
G14188742Courtesy of MERCEDES-BENZ USA

IMPORTANT Model 205.012/013/047/053/054/147/212/213/247/253, 253.311/354/911/954/99

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

Function requirements, general 

For regulating the climate control:

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

For cooling operation:

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.

For residual heat utilization (with code 228 (Stationary heater) or code 581 (Automatic air conditioning) or model 205.013/047/053/054/147/213/247/253, model 253.311/354/911/954/99):

Climate control, general 

The electronic temperature control and the air distribution in the vehicle interior take place depending on the settings selected on the air conditioning control panel, rear climate control operating unit (with code 581 (Automatic air conditioning)), Audio/COMAND® control panel (except code 446 (Touchpad only)) or touchpad (with code 446 (Touchpad only)) and the variables detected by the different sensors (e.g. vehicle interior temperature, outside temperature, coolant temperature, vehicle speed). Determination of these variables is described below.

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 

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. The outside temperature is only taken into account if the vehicle is driven for at least 30 s above 30 km/h. The last measured temperature value is used at speeds below 30 km/h as well as when the ignition is switched ON/OFF.

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.

On vehicles up to model year 2019, the overhead control panel control unit sends the vehicle interior temperature over the roof LIN to the front SAM control unit. The front SAM control unit sends this via the interior CAN to the climate control control unit. On vehicles as from model year 2019, the overhead control panel control unit sends the interior temperature to the climate control control unit over the interior CAN.

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 

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. In the case of an imminent fogging of the windshield, corresponding countermeasures such as the cut-in of the refrigerant compressor are initiated.

Coolant temperature 

The coolant temperature is recorded by the coolant temperature sensor.

Model 253.99:

The powertrain control unit reads in the signals of the coolant temperature sensor directly and sends information about the coolant

Except model 253.99:

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 control unit.

temperature over the suspension FlexRay, electronic ignition lock control unit and the interior CAN to the climate control control unit. The value is used to control the blend air flaps and to actuate the coolant circulation pump.

In model 205.013/047/053/054/147/213/247/253, model 253.311/354/911/954/99, the coolant temperature in the high-voltage PTC heater is also detected by the high-voltage PTC heater temperature sensor. The climate control control unit reads in the signals of the high-voltage PTC heater temperature sensor over the climate control LIN 2. The value is used to 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 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 deactivated or the front evaporator shutoff valve (model 205.012/013/047/053/054/147/212/213/247/253, model 253.311/354/911/954/99) is closed. From a temperature of 2.5°C, the refrigerant compressor is switched on again or the front evaporator shutoff valve (model 205.012/013/047/053/054/147/212/213/247/253, model 253.311/354/911/954/99) is reopened.

The temperature of 2.5°C is maintained for no longer than 20 min after the ignition has been switched on. The temperature (depending on the cooling requirement) is then regulated to between 3 and 8°C.

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. If the refrigerant pressure is less than 0.8 bar or more than 28 bar, the refrigerant compressor or electric refrigerant compressor is switched off or not switched in.

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 via the front air conditioning control LIN. 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 (except model 253.99) 

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 control unit. The engine speed is used to regulate the refrigerant compressor, among other things.

Door status 

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

The climate control control unit retains the current blower setting 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 the interior CAN to the A/C control unit:

The climate control control unit retains the current blower setting 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 A/C control unit via the interior CAN. The position of the panoramic sliding sunroof is transmitted by the panoramic sliding sunroof control unit to the A/C control unit via the interior CAN.

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

Position of the soft top (model 205.4) 

The position of the soft top is transmitted by the rear control unit via interior CAN to the climate control control unit.

Settings at the climate control operating unit 

The settings for the climate control of the driver and front passenger compartment can be adjusted using the following buttons at the climate control operating unit:

The settings are transmitted by the climate control operating unit via the climate control LIN to the A/C 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 A/C 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.

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.

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 setting options for the front air distribution can also be realized via the Audio/COMAND® control panel (except code 446 (Touchpad only)) or via the touchpad (with code 446 (Touchpad only)) and are displayed in 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.

Settings at the rear air conditioning operating unit (with code 581 (Automatic air conditioning)) 

The rear climate control functions can be adjusted at the rear air conditioning operating unit. The settings are transmitted by the rear air conditioning 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 air conditioning operating unit.

Settings on head unit 

The air conditioning system can be switched off or the air conditioning function selected using the menu in the head unit.

The operation is realized via the Audio/COMAND® control panel (except code 446 (Touchpad only)) or via the touchpad (with code 446 (Touchpad only)). 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 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.

VCS (with code 531 (COMAND® APS), model 253 as of model year 2020) 

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

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

VCS status (with code 531 (COMAND® APS), model 253 as of model year 2020) 

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 A/C control unit.

Actuation of the A/C components 

Actuation of the A/C components includes the following subfunctions:

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 climate control operating unit, the air is distributed via various air ducts and air outlets in the vehicle interior.

IMPORTANT Model 205

with code 531 (COMAND® APS)

Model 253 as of model year 2020

Model 253 up to model year 2020 with code 531 (COMAND® APS)

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

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

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

IMPORTANT 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 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 air conditioning operating unit. The air flow that now arrives in the rear is boosted by the booster blower electronic blower regulator. The climate control 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.

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

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 the front A/C control LIN:

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

The position of the defroster/footwell/center air vent flap is detected by the central air distribution position detection microswitch. The A/C 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 A/C control unit via the defroster/footwell/center air vent flap actuator motor. Vehicles with CODE 581 (Automatic air conditioning):

The climate control unit actuates the actuator motors via the front air conditioning control LIN.

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)

To prevent any fogging of the windows, the defroster flaps are closed and the footwell flaps are opened for a period of 2 min after circuit 15 has been switched off. After starting the vehicle the settings are all available again.

IMPORTANT When circuit 15 is 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 

G10134833Courtesy of MERCEDES-BENZ USA

Actuation of refrigerant compressor (except model 205.012/013/047/053/054/147/212/213/247/253, model 253.311/354/911/954/99) 

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 via the refrigerant compressor closed-loop control valve. The A/C system 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 A/C control unit directly actuates the refrigerant compressor with magnetic clutch.

The climate control 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)).

Actuation of electric refrigerant compressor (model 205.012/013/047/053/054/147/212/213/247/253, model 253.311/354/911/954/99) 

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.

Actuation of fan motor (engine fan) 

The fan motor is used for cooling the coolant and refrigerant. The climate control control unit calculates the nominal fan speed to match the refrigerant pressure.

Except model 253.99:

The climate control unit transmits a corresponding request via the interior CAN, electronic ignition lock control unit, suspension FlexRay, powertrain control unit and 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 calculates the nominal fan speed to match the engine temperature and actuates the fan motor accordingly.

Model 253.99:

The climate control unit transmits a corresponding request via the interior CAN, electronic ignition lock control unit and suspension FlexRay to the powertrain control unit. The powertrain control unit calculates the nominal fan speed to match the engine temperature and actuates the fan motor accordingly.

Actuation of PTC heater booster (diesel engine) 

When required, the PTC heater booster is switched on by the A/C 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).

Actuation of high-voltage PTC heater (model 205.013/047/053/054/147/213/247/253, model 253.311/354/911/954/99) 

When required, the high voltage PTC heater is switched on by the climate control 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 90°C. The water temperature is recorded by the high voltage PTC heater temperature sensor, and read in by the climate control control unit over the climate control LIN 2.

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.

Actuation of high-voltage PTC heater switchover valve (model 205.013/047/053/054/147/213/247/253, model 253.311/354/911/954/99) 

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 (except model 253.99) and the heater heat exchanger (small or large coolant circuit). The climate control unit transmits the high-voltage PTC heater switchover valve actuation request via the air conditioning control LIN 2 to the high-voltage PTC heater. The high-voltage PTC heater actuates the high-voltage PTC heater switchover valve directly.

Actuation of front evaporator shutoff valve (model 205.012/013/047/053/054/147/212/213/247/253, model 253.311/354/911/954/99) 

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

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

Actuation of coolant circulation pump 

The coolant circulation pump supplies the coolant through the heater core that dissipates the heat to the air blowing by.

At low engine rpm (except model 253.99), the coolant circulation pump is also actuated to provide the flow volume required to heat up the air flowing past. The coolant circulation pump is actuated directly by the A/C system control unit.

An actuation also takes place when the vehicle is switched off or in electric mode (model 205.012/013/047/053/054/147/212/213/247/253,

model 253.311/354/911/954/99).

Actuation of heating circuit circulation pump (model 205.013/047/053/054/147/213/247/253, model 253.311/354/911/954/99) 

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 heating circuit circulation pump is directly actuated by the high-voltage PTC heater, the climate control unit transmits the request via the air conditioning control LIN 2 to the high-voltage PTC heater.

Additional function requirements for actuation of ionizer (with code P21 (Air quality package)) 

Actuation of ionizer (with code P21 (Air quality package)) 

The ionizer serves for the 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 climate control unit actuates the ionizer via the air conditioning control LIN 2.

IMPORTANT Model 205 (except 205.012/013/047/053/054/147/212/213/247/253) with code 577 (Remote activation of heating and ventilation systems)

Model 205.012/013/047/053/054/147/212/213/247/253, 253.311/354/911/954/99

The ionizer can also be activated/deactivated via 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)) 

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 and creates its own, clean air flow. When the flask is inserted and the

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.

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 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. 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 205.012/013/047/053/054/147/212/213/247/253) with code 577 (Remote activation of heating and ventilation systems) Model 205.012/013/047/053/054/147/212/213/247/253, 253.311/354/911/954/99

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.

Actuation of high-voltage battery cooling 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 A/C system 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.

Actuation of high-voltage battery cooling expansion valve (model 205.013/047/053/054/147/213/247/253, model 253.311/354/911/954/99) 

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

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

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

Shift point adjustment (transmission 722.9 (except 722.930), 725 and except model 205.012/013/047/053/054/147/212/213/247/253, model 253.311/354/911/954/99) 

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 

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

Recirculated air mode 

The air-recirculation mode comprises the following subfunctions:

Air recirculation mode via the air recirculation mode button 

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

Vehicles without CODE 494 (USA version):

If the air recirculation mode button is pressed for longer than 1.5 s, the side windows and 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 again for longer than 1.5 s, the side windows and sliding roof (with code 414 (Sliding roof)) or the panoramic sliding sunroof (with code 413

The climate control unit reads in the status of the air-recirculation mode button via the air conditioning operating LIN and actuates the fresh air/ram air/air recirculation flap actuator motor via the front air conditioning control LIN.

(Panoramic sliding sunroof)) are moved back to their default positions (provided that they were not manually adjusted during air recirculation mode).

Additional function requirements for pollutant-controlled air-recirculation mode (except model 253.99, with code 581 (Automatic air conditioning)) 

Pollutant-controlled air-recirculation mode (except model 253.99, 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. From a certain pollutant concentration, the climate control unit actuates the fresh air/ram air/air recirculation flap actuator motor via the front air conditioning control LIN 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 after starting the vehicle, the condition for pollutant-sensitive air recirculation mode exists, then fresh air is initially supplied for 30 s. Following this, operation continues first with 80 % of pollutant-controlled air-recirculation mode and then, after 10 s, with 100 % pollutant-controlled air-recirculation mode as required.

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 30 minutes.

Additional function requirements for automatic air recirculation mode 

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 via the front A/C control LIN, 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 Automatic air recirculation mode is active for max. 30 min.

Defrost 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 

Evaporator drying 

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 vehicle is switched off. 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 this purpose, the blower is actuated at the slowest speed for 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.

Residual heat utilization (with code 228 (Stationary heater) or code 581 (Automatic air conditioning) or model 205.013/047/053/054/147/213/247/253, model 253.311/354/911/954/99) 

The function is switched on by pressing the climate control and residual heat ON/OFF menu button (with code 228 (Stationary heater) or with code 581 (Automatic air conditioning)) or the "A/C" and residual heat ON/OFF button on the climate control operating unit. 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.

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 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 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 
scientia non olet · About LEMON Manuals