Climate control regulation, function

P83.40-5332-79

P83.40-5333-79

Function requirements, general

For regulating the climate control:

 Terminal 15 ON

 Air conditioning switched on

For cooling operation:

 Engine running (except model 166.063)

 Refrigerant compressor ON

For evaporator drying process:

 Engine Off

For residual heat utilization (except code 494 (USA version)):

 Terminal 15 Off or terminal 15C Off

 The electronic ignition lock control unit transmits the status of circuit 15 to the automatic air conditioning control and operating unit via the interior CAN.
The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" signal via chassis CAN 1, electronic ignition lock control unit and interior CAN to the automatic air conditioning control and operating unit.

 Model 166.063
as of model year 2016
The ME-SFI [ME] control unit sends the "Engine running" signal via drive train CAN, powertrain control unit, chassis CAN 1, electronic ignition lock control unit and interior CAN to the automatic air conditioning control and operating unit.

Climate control, general

The electronic temperature control and the air distribution in the vehicle interior take place depending on the settings made at the automatic air conditioning control and operating unit, the RCP [HBF] control unit (with code 581 (Automatic air conditioning)) and on the variables recorded by different sensors (e.g. interior temperature, outside temperature, coolant temperature, vehicle speed).

The automatic air conditioning control and operating unit is networked with the vehicle electronics system via interior CAN, climate control LIN, climate control LIN 1 and climate control LIN 2. This in turn makes it possible to incorporate relevant parameters in order to improve regulation quality and to lower power consumption.

The automatic air conditioning control function encompasses the following subfunctions:

 Function sequence for recording and evaluating variables

 Function sequence for AC component actuation

 Function sequence for shift point adjustment (except model 166.063)

 Fresh air mode function sequence

 Air recirculation mode function sequence

 Function sequence for defroster function

 Function sequence for evaporator drying process

 Function sequence for residual heat utilization

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

 Function sequence for maximum cooling output (with CODE 494 (USA version))

Function sequence for recording and evaluating variables

The following variables are recorded and evaluated:

 Outside temperature

 Interior temperature in head area

 Air outlet temperature in rear head area (model 166.8 with CODE 582 (Rear air conditioning system))

 Temperature at the air outlets in the vehicle

 Temperature and moisture on windshield

 Coolant temperature

 Temperature on evaporator

 Temperature at evaporator of rear air conditioning (model 166.8 with CODE 582 (Rear air conditioning system))

 Refrigerant pressure

 Solar radiation

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

 Vehicle speed

 Engine speed

 Door status

 Side window position

 Position of sliding roof [SD] (with CODE 414 (Sliding roof)) or panoramic sliding sunroof (with CODE 413 (Panoramic sliding sunroof))

 Settings on rear control panel (RCP) control unit (with CODE 581 (Automatic air conditioning))

 Settings at the radio (with CODE 505 (Radio 20 NTG5 non-navigation-capable) or CODE 522 (Audio 20 radio)) or at the COMAND controller unit (with CODE 531 (COMAND APS))

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

Outside temperature

The outside temperature sensor measures the outside temperature. The SAM control unit reads in the outside temperature sensor signal directly, calculates the outside temperature and sends this via interior CAN to the automatic air conditioning control and operating unit. The automatic air conditioning control and operating unit requires this value to reach the desired interior temperature by adjusting the blend air flaps accordingly.

 If the vehicle is stationary, the measured temperature can differ considerably from the outside temperature. The outside temperature is therefore only integrated in the control process if the vehicle speed exceeds v = 20 km/h for a minimum time of t = 20 s. At speeds of v < 20 km/h and when the ignition is switched off and on, the temperature value last measured is used.

Interior temperature in head area

The interior temperature is recorded by the interior temperature sensor with integrated fan in the overhead control panel control unit. The SAM control unit reads in the interior temperature over the roof LIN and sends this over the interior CAN to the automatic air conditioning control and operating unit.

Air outlet temperature in rear head area (model 166.8 with CODE 582 (Rear air conditioning system))

The air outlet temperature in the head area in the rear is recorded by the rear air conditioning head area temperature sensor. The signals of the rear air conditioning head area temperature sensor are read in directly by the automatic air conditioning control and operating 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 automatic air conditioning control and operating unit. The automatic air conditioning control and operating unit regulates the air outlet temperature at the respective 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 rain/light sensor with additional functions directly reads in the signals of the humidity and temperature sensor and sends the dew point temperature via the roof LIN, SAM control unit and interior CAN to the automatic air conditioning control and operating unit. If the windows threaten to fog up, corresponding countermeasures are taken such as, e.g. switching on the refrigerant compressor.

Coolant temperature

The coolant temperature is recorded by the coolant temperature sensor. The CDI control unit or ME-SFI [ME] control unit reads in the signals of the coolant temperature sensor directly, uses this to calculate the coolant temperature and sends this via chassis CAN 1, electronic ignition lock control unit and interior CAN to the automatic air conditioning control and operating unit. On model 166.063, the ME-SFI [ME] control unit sends the coolant temperature via drive train CAN, powertrain control unit, chassis CAN 1, electronic ignition lock control unit and interior CAN to the automatic air conditioning control and operating unit.

On model 166.063, the coolant temperature in the high-voltage PTC heater is also recorded by the high-voltage PTC heater temperature sensor. The automatic air conditioning control and operating unit reads in the signals of the high-voltage PTC heater temperature sensor via climate control LIN 2.

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

Temperature on evaporator

To prevent the evaporator from icing up, the temperature there is recorded by the evaporator temperature sensor. The signals of the evaporator temperature sensor are read in directly by the automatic air conditioning control and operating unit. If the evaporator temperature drops to approx. T  2 °C , the refrigerant compressor or the electric refrigerant compressor is switched off or the respective shutoff valve is closed.

Temperature at evaporator of rear air conditioning (model 166.8 with CODE 582 (Rear air conditioning system))

To prevent the evaporator of the rear air conditioning from icing up, the temperature there is recorded by the rear air conditioning evaporator temperature sensor. The signals of the rear air conditioning evaporator temperature sensor are read in directly by the automatic air conditioning control and operating unit. If the evaporator temperature drops to around T  2 °C the flow of refrigerant to the evaporator in the rear is closed off by the rear air conditioning system evaporator shutoff valve. The automatic air conditioning control and operating unit actuates the rear air conditioning evaporator shutoff valve directly.

Refrigerant pressure

The refrigerant pressure is recorded by the refrigerant pressure sensor. The refrigerant pressure sensor signals are read in directly by the automatic air conditioning control and operating unit. The pressure is compared with a temperature/pressure curve stored in the automatic air conditioning control and operating unit. At a refrigerant pressure of p < 1.7 bar or p > 30 bar, the refrigerant compressor is switched off or not activated.

Solar radiation

The sun sensor records the intensity of the solar radiation on the vehicle. The automatic air conditioning control and operating unit reads in the signals from the sun sensor directly and adapts the interior temperature and the blower output 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 values are read in directly by the AAC control and operating unit via the climate control LIN. The automatic air conditioning control and operating unit implements the automatic recirculation according to the read-in values.

Vehicle speed

The vehicle speed is transmitted by the instrument cluster to the automatic air conditioning control and operating unit via the interior CAN. 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 read in by the CDI control unit or ME-SFI [ME] control unit and sent via chassis CAN 1, electronic ignition lock control unit and interior CAN to the automatic air conditioning control and operating unit. The engine speed is used among other things to regulate the respective refrigerant compressor. On model 166.063, the ME-SFI [ME] control unit sends the engine speed via drive train CAN, powertrain control unit, chassis CAN 1, electronic ignition lock control unit and interior CAN to the automatic air conditioning control and operating unit.

Door status

The status of each door is determined by the following control units and transmitted via the interior CAN to the automatic air conditioning control and operating unit:

 Left front door control unit

 Right front door control unit

 Left rear door control unit

 Right rear door control unit

The automatic air conditioning control and operating unit retains the current blower output when a door is open in order to avoid unnecessary readjustment in the event of large differences between the interior temperature and outside temperature.

Side window position

The position of the respective side window is determined by the following control units and transmitted via interior CAN to the automatic air conditioning control and operating unit:

 Left front door control unit

 Right front door control unit

 Left rear door control unit

 Right rear door control unit

The automatic air conditioning control and operating unit retains the current blower output when a side window is open in order to avoid unnecessary readjustment in the event of large differences between the interior temperature and outside temperature.

Position of sliding roof [SD] (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 via the interior CAN to the automatic air conditioning control and operating unit. The position of the panoramic sliding sunroof is sent by the panoramic sliding sunroof control unit in the panoramic sliding sunroof control module via interior CAN to the automatic air conditioning control and operating unit.

The automatic air conditioning control and operating unit retains the current blower output when the panoramic sliding sunroof is open in order to avoid unnecessary readjustment in the event of large differences between the interior temperature and outside temperature.

Settings on rear control panel (RCP) control unit (with CODE 581 (Automatic air conditioning))

The climate control of the rear compartment can be set by the rear occupants via the RCP [HBF] control unit. The selected settings are sent by the RCP [HBF] control unit via interior CAN to the automatic air conditioning control and operating unit for processing. This data is used to regulate the air volume, the air distribution and the temperature in the rear. The settings selected are shown on the display of the RCP [HBF] control unit.

Settings at the radio (with CODE 505 (Radio 20 NTG5 non-navigation-capable) or CODE 522 (Audio 20 radio)) or at the COMAND controller unit (with CODE 531 (COMAND APS))

The air conditioning can be switched off or the air conditioning functions selected using the menu in the radio or in the COMAND controller unit. The Audio/COMAND operating unit is used to operate it. The control signals are read in by the radio or the COMAND controller unit via telematics CAN and sent via interior CAN to the automatic air conditioning control and operating unit.

The radio or the COMAND controller unit generates the corresponding picture data and sends a switch-on request over the telematics CAN to the Audio/COMAND display. 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 COMAND controller unit sends the status of the VCS [SBS] to the automatic air conditioning control and operating unit via interior CAN.

Function sequence for AC component actuation

The function sequence for actuation of the air conditioning components consists of the following subfunctions:

 Function sequence for actuation of blower motor

 Function sequence for actuation of rear blower motor (with CODE 581 (Automatic air conditioning))

 Function sequence for actuation of rear air conditioning blower motor (model 166.8 with CODE 582 (Rear air conditioning system))

 Function sequence for actuation of the air ducting flaps

 Function sequence for actuation of the refrigerant compressor (except model 166.063)

 Function sequence for actuation of electric refrigerant compressor (model 166.063)

 Function sequence for actuation of the fan motor

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

 Function sequence for actuation of high voltage PTC heater (model 166.063)

 Function sequence for actuation of front evaporator shutoff valve (model 166.063 or CODE 582 (Rear air conditioning system))

 Function sequence for actuation of rear air conditioning system evaporator shutoff valve (model 166.8 with CODE 582 (Rear air conditioning system))

 Function sequence for actuation of coolant circulation pump

 Function sequence for actuation of driver side air vent ionizer (with CODE P21 (Air quality package))

 Function sequence for actuation of high-voltage battery cooling system expansion valve (model 166.063)

Function sequence for actuation of blower motor

Ventilation of the vehicle interior is achieved with the aid of the blower motor. The automatic air conditioning control and operating unit forwards the request via climate control LIN 1 to the blower regulator, which then directly actuates the blower motor.

 The blower motor drives a radial blower which circulates the air in the vehicle interior or which supplies fresh air to the vehicle interior. This 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 the automatic air conditioning control and operating unit, the air is routed through various air ducts and air outlets into the vehicle interior.

 Model 166
as of model year 2016
with code 531 (COMAND APS)
Model 292
with code 531 (COMAND APS)
With VCS [SBS] active, the blower output is limited.

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

Function sequence for actuation of rear blower motor (with CODE 581 (Automatic air conditioning))

The rear blower motor is used for better ventilation of the rear compartment. Depending on the settings on the automatic air conditioning control and operating unit and on the RCP [HBF] control unit, the automatic air conditioning control and operating unit forwards the request directly to the booster blower electronic blower regulator, which then actuates the rear blower motor.

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

Function sequence for actuation of rear air conditioning blower motor (model 166.8 with CODE 582 (Rear air conditioning system))

The rear air conditioning blower motor is used to route fresh air or interior air through the rear climate control box into the rear. Depending on the settings on the automatic air conditioning control and operating unit and on the RCP [HBF] control unit, the automatic air conditioning control and operating unit forwards the request via climate control LIN 1 to the rear air conditioning electronic blower regulator, which then actuates the rear air conditioning blower motor.

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

Function sequence for actuation of the air ducting flaps

The air distribution in the vehicle interior is controlled by adjusting the air ducting flaps in the air conditioner housing.

Vehicles with CODE 580 (Air conditioning):

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

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

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

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

Vehicles with CODE 581 (Automatic air conditioning):

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

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

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

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

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

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

 Rear blend air flap with blocking function via rear blend air flap actuator motor with blocking function (ventilation control)

 Left B-pillar air distribution via left B-pillar air distribution actuator motor (ventilation control)

 Right B-pillar air distribution via right B-pillar air distribution actuator motor (ventilation control)

 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 air distribution flap via rear air distribution flap actuator motor (ventilation control)

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

The automatic air conditioning control and operating unit actuates the actuator motors via climate control LIN.

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

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

 With circuit 15 OFF, when one of the doors is opened the fresh air/recirculated air flap is moved by the fresh air/recirculated air flap actuator motor to 50 %. The door closing forces are thereby reduced. The function can be set with the diagnostic tester.

 Model 166
as of model year 2016
with code 581 (Automatic air conditioning)
Model 292
with code 581 (Automatic air conditioning)
The rear air distribution flap is always held at an opening angle of 0 to 50% to ensure a sufficient supply of air to the air outlets in the footwell and at the B-pillars.

 Model 166
as of model year 2016
with code 581 (Automatic air conditioning)
Model 292
with code 581 (Automatic air conditioning)
Additional air outlets are present in the paneling of the B-pillar.

 Model 166.8
as of model year 2016
Additional air outlets are present in the headliner in the rear.

P83.10-2770-76

Function sequence for actuation of the refrigerant compressor (except model 166.063)

The refrigerant compressor is responsible for induction and compression of the refrigerant. The refrigerant compressor is actuated continuously up to 100 % by the automatic air conditioning control and operating unit via the compressor control valve. The automatic air conditioning control and operating unit actuates the compressor control 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 automatic air conditioning control and operating unit directly actuates the refrigerant compressor with magnetic clutch.

The automatic air conditioning control and operating unit also sends the request for idle speed increase via interior CAN, electronic ignition lock control unit and chassis CAN 1 to the ME-SFI [ME] control unit or the CDI control unit. This increases the idle speed in accordance with the additional load that occurs when the refrigerant compressor is switched on.

 The refrigerant compressor can be switched on and off by pressing the "A/C" button or the "OFF" button (with CODE 581 (Automatic air conditioning)) on the automatic air conditioning control and operating unit.

 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 166.063)

The electric refrigerant compressor is responsible for intake and compression of the refrigerant. The electric refrigerant compressor is actuated by the automatic air conditioning control and operating unit via climate control LIN 2.

 The electric refrigerant compressor can be switched on and off by pressing the "A/C" button or the "OFF" button (with CODE 581 (Automatic air conditioning)) on the automatic air conditioning control and operating unit.

 In the event of an accident, the high-voltage components are switched off by the battery management system control unit (N82/2).

Function sequence for actuation of the fan motor

The fan motor is used for cooling the coolant and refrigerant. The automatic air conditioning control and operating unit calculates the specified fan speed depending on the refrigerant pressure and sends the request via interior CAN, electronic ignition lock control unit and chassis CAN 1 to the CDI control unit or the ME-SFI [ME] control unit. On model 166.063, the automatic air conditioning control and operating unit sends the request via interior CAN, electronic ignition lock control unit, chassis CAN 1, powertrain control unit and drive train CAN to the ME-SFI [ME] control unit.

The CDI control unit or the ME-SFI [ME] control unit then calculates the specified fan speed depending on the engine temperature, compares this with the air conditioning request and then directly actuates the fan motor.

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

The PTC heater booster makes it possible to heat up the vehicle interior quickly. The PTC heater booster is switched on and off as required by the automatic air conditioning control and operating unit via the climate control LIN.

 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 166.063)

The high-voltage PTC heater is activated as required by the automatic air conditioning control and operating unit via climate control LIN 2. To protect the high-voltage PTC heater against damage, this is switched off at a coolant temperature of T > 90 °C. The coolant temperature is recorded by the high-voltage PTC heater temperature sensor.

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

Function sequence for actuation of front evaporator shutoff valve (model 166.063 or CODE 582 (Rear air conditioning system))

The front evaporator shutoff valve is used to control the flow of refrigerant to the front evaporator. Actuation depends on the cooling request. The automatic air conditioning control and operating unit actuates the front evaporator shutoff valve directly.

Function sequence for actuation of rear air conditioning system evaporator shutoff valve (model 166.8 with CODE 582 (Rear air conditioning system))

The rear air conditioning evaporator shutoff valve is used to control the infeed of refrigerant to the rear air conditioning evaporator. Actuation depends on the cooling request. The automatic air conditioning control and operating unit actuates the rear air conditioning evaporator shutoff valve directly.

Function sequence for actuation of coolant circulation pump

The coolant circulation pump circulates the coolant in the engine cooling circuit. In the process, it absorbs engine heat. The heated coolant passes through the heater heat exchanger, which dissipates heat to the air blowing by.

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 automatic air conditioning control and operating unit. Actuation also takes place at engine stop (with CODE B03(ECO start/stop function)).

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 interior air of the vehicle is cleaned and refreshed using the "Ionization“ function .

The radio or the COMAND controller unit sends the "Switch on ionization" request via interior CAN to the automatic air conditioning control and operating unit. The automatic air conditioning control and operating unit actuates the driver side air vent ionizer via climate control LIN 2.

 The ionization function can only be activated over the climate menu in the radio or the COMAND controller unit.

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

Function sequence for actuation of high-voltage battery cooling system expansion valve (model 166.063)

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 status of the shutoff valve (open/closed) via chassis CAN 1, electronic ignition lock control unit and interior CAN to the automatic air conditioning control and operating unit.

Function sequence for shift point adjustment (except model 166.063)

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

The automatic air conditioning control and operating unit sends the request for a shift point adjustment via interior CAN, electronic ignition lock control unit, chassis CAN 1, CDI control unit or ME-SFI [ME] control unit and drive train CAN to the fully integrated transmission control unit.

Fresh air mode function sequence

The fresh air/recirculated air flap is open and fresh air is delivered into the vehicle interior through the air conditioner housing.

Air recirculation mode function sequence

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

 Function sequence for air recirculation mode using air recirculation mode button

 Function sequence for pollutant-sensitive air recirculation mode (with CODE 581 (Automatic air conditioning))

Function sequence for air recirculation mode using air recirculation mode button

When the air recirculation mode button on the automatic air conditioning control and operating unit is pressed for t < 1.5 s, the fresh air/recirculated air flap is closed to prevent air entering from outside. The air only circulates in the vehicle interior and unpleasant odors and harmful gases are kept out. The LED above the air recirculation mode button lights up during air recirculation mode.

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

If the air recirculation mode button is pressed for t > 1.5 s, the side windows and the sliding roof or the 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 or the panoramic sliding sunroof are moved back to the default position (provided that they were not manually adjusted during air recirculation mode).

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

 Refrigerant compressor SWITCHED ON

Function sequence for pollutant-sensitive air recirculation mode (with CODE 581 (Automatic air conditioning))

The air quality sensor sends the pollutant values of the outside air via climate control LIN to the automatic air conditioning control and operating unit. Starting from a certain pollutant concentration, the recirculated air flap is automatically set to the recirculated air position. The automatic air conditioning control and operating unit actuates the fresh air/recirculated air flap actuator motor via the climate control LIN. 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 another t = 10 s, as required, with 100 % pollutant-controlled air recirculation mode.

 The pollutant-controlled air recirculation mode is not indicated by the LED in the air recirculation mode button.

Function sequence for defroster function

When the defroster button is pressed, all air flaps are closed with the exception of the defroster flaps and the fresh air/recirculated air flap. These are fully opened. The LED integrated in the defroster button lights up as feedback. The defroster flaps are adjusted so that the maximum air flow is directed to the windshield and the front side windows. The blend air flap is set to full warm air supply. The automatic air conditioning control and operating unit regulates via climate control LIN 1 the blower regulator and this in turn regulates the blower motor such that an optimum defrost mode is achieved depending on the outflow 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

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

 Outside temperature T > 20 °C

 Doors closed

 Doors closed

 Kilometer reading > 250 km

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.

After the engine is switched off, the automatic air conditioning control and operating unit sends the signal to activate the evaporator drying process timer via interior CAN to the instrument cluster. The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" signal via chassis CAN 1, electronic ignition lock control unit and interior CAN to the automatic air conditioning control and operating unit. On model 166.063, the ME-SFI [ME] control unit sends the "Engine running" signal via drive train CAN, powertrain control unit, chassis CAN 1, electronic ignition lock control unit and interior CAN to the automatic air conditioning control and operating unit.

After a waiting time of t = 1 h the instrument cluster transmits the request for the evaporator drying process via the interior CAN to the AAC control and operating unit which then starts the evaporator drying process. For this purpose, the blower is actuated at the slowest speed for t = 30 min.

The automatic air conditioning control and operating unit sends the request via climate control LIN 1 to the blower regulator. The blower regulator actuates the blower motor at the lowest blower stage. The air supply serves to reduce residual moisture in the evaporator.

Function sequence for residual heat utilization

Pressing the "REST" or the "A/C REST" button on the AAC control and operating unit switches on the function. The automatic air conditioning control and operating unit actuates the coolant circulation pump directly. The coolant circulation pump delivers the coolant that is still warm through the heater heat exchanger.

At the same time, the automatic air conditioning control and operating unit sends the "ventilate" request via climate control LIN 1 to the blower regulator, which then actuates the blower motor with reduced output.

The air drawn in by the blower motor is routed along the heater heat exchanger and thus heated up. The function is terminated after a time of t = 30 min. has elapsed or when the on-board power supply voltage drops below a certain value.

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

To prevent the ingress of noxious gases into the vehicle interior in the event of an accident, the automatic air conditioning control and operating unit starts the following activities:

 The blower motors are no longer actuated. Air is not circulated in the vehicle interior.

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

 The refrigerant compressor regulating valve is switched off (model 166 (except model 166.063) and model 292 except CODE B09 (Refrigerant compressor with magnetic clutch)) . The refrigerant compressor no longer circulates the refrigerant.

 The refrigerant compressor magnetic clutch is opened (with CODE B09 (Refrigerant compressor with magnetic clutch)). The refrigerant compressor is no longer driven.

 The electric refrigerant compressor is no longer energized (model 166.063).

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

 The high voltage PTC heater (on model 166.063) is switched off.

The supplemental restraint system control unit sends the crash signal via chassis CAN 1, electronic ignition lock control unit and interior CAN to the automatic air conditioning control and operating unit.

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

Function sequence for maximum cooling output (with CODE 494 (USA version))

By pressing the "MAX COOL" button on the automatic air conditioning control and operating unit, the blower output is raised to 100% and the temperature is set to "maximum cold".