Climate control regulation, function

Networking

In vehicles as of model year 2016, there are two variants of the chassis CAN (CAN E).

Variant 1:

If the vehicle does not have any of the equipment codes specified in Variant 2, then, as before, only one chassis CAN is available.

Version 2:

If the vehicle has one of the following equipment codes, then one chassis CAN 1 (CAN E1) and one chassis CAN 2 (CAN E2) is available:

 CODE 218 (Reversing camera)

 code 234 (Blind Spot Assist)

 CODE 459 (Steel suspension with adjustable damping)

 CODE 475 (Tire pressure monitor)

 CODE 476 (Lane Keeping Assist)

 Code 513 (Traffic Sign Assist)

 CODE 614 (Bi-xenon headlamp)

 CODE 615 (Bi-xenon headlamps with active curve lights)

 CODE 618 (Bi-xenon headlamps)

 CODE 621 (Intelligent Light System (left-hand traffic))

 code 622 (Intelligent Light System)

 CODE 631 (Static LED headlamps for left-hand traffic system)

 CODE 632 (Static LED headlamps for right-hand traffic system)

The differences between variant 1 and variant 2 are explained in the following text. Vehicles up to model year 2016 are assigned to Variant 1.

P83.40-5081-79

Function requirements, general

For regulating the climate control:

 Terminal 15 ON

 Automatic air conditioning switched on

For cooling operation:

 Engine running (except model 242.890)

 Refrigerant compressor switched on (except CODE B09 (Refrigerant compressor with magnetic clutch))

 Refrigerant compressor with magnetic clutch switched on (with CODE B09 (Refrigerant compressor with magnetic clutch))

 Electric refrigerant compressor switched on (model 242.890)

For evaporator drying process:

 Engine Off

For residual heat utilization (with CODE 581 (Automatic air conditioning) and except CODE 494 (USA version)):

 Circuit 15C ON or circuit 15R ON

 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 (engine 651) or the ME-SFI [ME] control unit (engine 270 and 133) transmits the "engine running" signal via the chassis CAN (variant 1) or chassis CAN 1 (variant 2), the electronic ignition lock control unit and the interior CAN to the automatic air conditioning control and operating unit.
With engine 607, the CDI control unit transmits the "engine running" signal via the drivetrain CAN, the powertrain control unit, the chassis CAN (variant 1) or chassis CAN 1 (variant 2), the electronic ignition lock control unit and the interior CAN to the automatic air conditioning control and operating unit.
In model 242.890, the powertrain control unit transmits the "drivetrain operational" signal via the chassis CAN (variant 1) or chassis CAN 1 (variant 2), the electronic ignition lock control unit and the 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 are carried out depending on the settings at the automatic air conditioning control and operating unit and the variables measured by various sensors (e.g. interior temperature, outside temperature, coolant temperature, vehicle speed). Determination of these variables is described below.

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

 Model 117, 156, 242, 246
Model 176
except code 516 (Audio 5 USB)
If settings are altered on the automatic air conditioning control and operating unit that affect the temperature, the air distribution or the air flow, then the relevant adjustment values are shown briefly in the Audio/COMAND display (A40/8).

The climate control regulation function encompasses the following subfunctions:

 Function sequence for recording and evaluating variables

 Function sequence for AC component actuation

 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 (with CODE 581 (Automatic air conditioning) and except CODE 494 (USA version))

 Function sequence for shutoff of the air conditioning system after an accident (crash signal transmitted) as of 01.06.2013

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

Function sequence for recording and evaluating variables

In addition to the settings made at the automatic air conditioning control and operating unit, the following variables are recorded and evaluated:

 Outside temperature

 Interior temperature

 Temperature and air humidity at the windshield (with CODE B03 (ECO start/stop function))

 Coolant temperature

 Temperature on evaporator

 Refrigerant pressure

 Refrigerant vacuum at refrigerant compressor (model 242.890)

 Solar radiation (with CODE 581 (Automatic air conditioning))

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

 Vehicle speed

 Engine speed (except model 242.890)

 Door status

 Side window position

 Status of voice control system (VCS [SBS]) (with CODE 512 (COMAND APS with DVD changer) or CODE 527 (COMAND APS with single DVD drive (with navigation)) or CODE 531 (COMAND APS) or CODE 532 (COMAND Japan))

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 included in the control if the vehicle speed is v > 20 km/h. The previously measured temperature is used at speeds of v < 20 km/h and when the ignition is being switched on and off.

Interior temperature

The interior temperature is recorded as follows:

 Interior temperature in the roof area:

The interior temperature sensor with integrated fan in the overhead control panel control unit records the interior temperature in the roof area. The overhead control panel control unit transmits the interior temperature via the roof LIN to the SAM control unit. The SAM control unit transmits this via the interior CAN to the automatic air conditioning control and operating unit. The fan sucks in the air for temperature measurement from the vehicle interior.

 Interior temperature in the instrument panel area (with CODE 581 (Automatic air conditioning)):

The interior temperature sensor records the interior temperature in the instrument panel area. The automatic air conditioning control and operating unit reads in the signals of the interior temperature sensor directly. The fan integrated in the interior temperature sensor draws in air for measuring the temperature from the vehicle interior.

 The fans provide continuous circulation of the interior air at the interior temperature sensors. This ensures that the temperature measurement is extremely accurate. Temperature control that is almost independent of the flow conditions in the vehicle interior is therefore possible. A mean value is calculated from the measurements of the interior temperature sensors. This mean value and the value of the outside temperature sensor are compared with a characteristics map stored in the automatic air conditioning control and operating unit, and used to control the interior temperature.

The mean value of the interior temperature is maintained in the following situations by the automatic air conditioning control and operating unit:

 Side window open

 Door open

This ensures that the air conditioning system immediately continues operating at the set specified temperature.

 Model 117, 156, 176, 242, 246
with code 581 (Automatic air conditioning)
The interior temperature is controlled by actuation of the left blend air flap actuator motor for the driver and by actuation of the right blend air flap actuator motor for the front passenger.

 Model 117, 156, 176, 242, 246
except code 581 (Automatic air conditioning)
The interior temperature is controlled by actuation of the left blend air flap actuator motor for both the driver and the front passenger.

Temperature and air humidity at the windshield (with CODE B03 (ECO start/stop function))

Model 117 (except model 117.9), 156 and model 176 up to 31.08.2015 and model 242, 246 up to 02.11.2014:

The vehicle interior humidity and temperature sensor measures the relative air humidity and temperature directly at the inside of the windshield. This data is used to calculate the dew point temperature. The SAM control unit reads in the signals of the vehicle interior humidity and temperature sensor via the roof LIN.

Model 117.9 and model 242, 246 as of 03.11.2014 and model 176 as of 01.09.2015:

The humidity and temperature sensor in the light sensor (except CODE 345 (Windshield wiper with rain sensor)) or in the rain/light sensor (with CODE 345 (Windshield wiper with rain sensor)) measures the relative air humidity and temperature directly on the inside of the windshield. The light sensor (except CODE 345 (Windshield wiper with rain sensor)) or the rain/light sensor (with CODE 345 (Windshield wiper with rain sensor)) directly reads in the signals of the humidity and temperature sensor and transmits the dew point temperature via the roof LIN, the SAM control unit, and the interior CAN to the automatic air conditioning control and operating unit.

If there is a risk of the windows fogging up, appropriate countermeasures are taken such as switching on the refrigerant compressor or starting the engine (with CODE B03 (ECO start/stop function)).

Coolant temperature

The coolant temperature sensor records the temperature of the coolant. The CDI control unit (engine 651) or the ME-SFI [ME] control unit (engine 133, 270) reads in the signals of the coolant temperature sensor directly, calculates the coolant temperature and transmits this via the chassis CAN (variant 1) or chassis CAN 1 (variant 2), the electronic ignition lock control unit and the interior CAN to the automatic air conditioning control and operating unit.

With engine 607, the CDI control unit transmits the coolant temperature via the drivetrain CAN, the powertrain control unit, the chassis CAN (variant 1) or chassis CAN 1 (variant 2), the electronic ignition lock control unit and the interior CAN to the automatic air conditioning control and operating unit.

In model 242.890, the automatic air conditioning control and operating unit reads in the signals of the high-voltage PTC heater temperature sensor via the climate control LIN.

The coolant temperature is used to control the blend air flaps and to actuate the coolant circulation pump (with CODE 581 (Automatic air conditioning) and except CODE 494 (USA version) and except model 242.890) or the heater circuit circulation pump (model 242.890).

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 approximately T = 2 °C, the refrigerant compressor is switched off in model 117, 156, 176, 242 (except model 242.890), 246. On model 242.890, the high-voltage battery cooling system shutoff valve and the front evaporator shutoff valve are actuated accordingly. This allows the high-voltage battery cooling to continue.

Refrigerant pressure

The refrigerant pressure sensor measures the pressure of the refrigerant. The refrigerant pressure is compared with a stored temperature/pressure curve. The refrigerant compressor is switched off or not re-activated at a refrigerant pressure of p < 1.7 bar and p > 28 bar. The refrigerant pressure sensor signals are read in directly by the automatic air conditioning control and operating unit.

Refrigerant vacuum at refrigerant compressor (model 242.890)

The refrigerant compressor vacuum sensor records the refrigerant vacuum upstream of the refrigerant compressor (low-pressure side).

To protect the electric refrigerant compressor from excessively high hot-gas temperatures and excessively low suction pressures, the refrigerant compressor rotational speed is limited by the refrigerant compressor vacuum sensor according to the following characteristic:

 p < 0.7 bar = refrigerant compressor off

 p = 0.9 bar = maximum n = 3000 rpm

 p = 1.1 bar = maximum n = 4500 rpm

 p = 1.2 bar = maximum n = 5500 rpm

 p = 1.5 bar = maximum n = 9000 rpm

The refrigerant compressor vacuum sensor signal is read in directly by the thermal management control unit and transmitted to the automatic air conditioning control and operating unit via the electric drive CAN, the gateway powertrain control unit, the vehicle CAN, the powertrain control unit, the chassis CAN (variant 1) or chassis CAN 1 (variant 2), the electronic ignition lock control unit and the interior CAN.

Solar radiation (with CODE 581 (Automatic air conditioning))

The sun sensor records the angle of incidence and the intensity of the solar radiation in the vehicle.

The automatic air conditioning control and operating unit reads in the signals of the sun sensor directly.

The interior temperature and the fan speed are adapted in accordance with these values. 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 following environmental influences:

 Contamination of the outside air with carbon monoxide (CO)

 Contamination of the outside air with nitrogen oxide (NOx)

The air quality sensor also records the following values:

 Outside temperature

 Relative humidity

 Outside dew point temperature

The automatic air conditioning control and operating unit reads in the data of the air quality sensor via the climate control LIN, assesses this and controls the air recirculation function in accordance with these values.

Vehicle speed

The instrument cluster transmits the vehicle speed via the interior CAN to the automatic air conditioning control and operating unit. The vehicle speed is used to control the ram air function and for internal calculation of the outside temperature.

Engine speed (except model 242.890)

The CDI control unit (engine 651) or the ME-SFI [ME] control unit (engine 133, 270) transmits the engine rpm via the chassis CAN (variant 1) or chassis CAN 1 (variant 2), the electronic ignition lock control unit and the interior CAN to the automatic air conditioning control and operating unit. With engine 607, the CDI control unit transmits the engine rpm via the drivetrain CAN, the powertrain control unit, the chassis CAN (variant 1) or chassis CAN 1 (variant 2), the electronic ignition lock control unit and the interior CAN to the automatic air conditioning control and operating unit.

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

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:

 SAM control unit

 Left front door control unit

 Right front door control unit

If the door is open, the automatic air conditioning control and operating unit maintains the current blower output in order to avoid unnecessary readjustment in the event of large differences between the air temperature inside and outside the vehicle.

Side window position

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

 SAM control unit

 Left front door control unit

 Right front door control unit

Status of VCS (with CODE 512 (COMAND APS with DVD changer) or CODE 527 (COMAND APS with single DVD drive (with navigation)) or CODE 531 (COMAND APS) or CODE 532 (COMAND Japan))

With active voice control system, the blower output of the blower regulator is limited. 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 air ducting flaps

 Function sequence for actuation of refrigerant compressor (except model 242.890)

 Function sequence for actuation of electric refrigerant compressor (model 242.890)

 Function sequence for fan motor actuation

 Function sequence for actuation of the coolant circulation pump (with CODE 581 (Automatic air conditioning) and except CODE 494 (USA version))

 Function sequence for actuation of heater circuit circulation pump (model 242.890)

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

 Function sequence for actuation of the front evaporator shutoff valve (model 242.890)

 Function sequence for actuation of high-voltage battery cooling system shutoff valve (model 242.890)

 Function sequence for actuation of the high voltage PTC heater (model 242.890)

Function sequence for actuation of blower motor

Ventilation is achieved with the aid of the blower motor. The AAC control and operating unit transmits the request to the blower regulator via the climate control LIN, which then actuates the blower motor.

 The blower motor drives a radial blower which circulates the air in the vehicle interior or which supplies fresh air to the vehicle interior. This prevents the glass panes from fogging up, supplies air to the vehicle occupants and enables 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.

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

 Model 117 as of 6/1/13, 156 as of 6/1/13, 176 as of 6/1/13, 242 as of 6/1/13, 246 as of 6/1/13
The blower motor is switched off in the event of an accident (crash signal sent).

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 automatic air conditioning control and operating unit actuates the following components via climate control LIN:

Vehicles with CODE 580 (Air conditioning):

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

 Blend air flap via left blend air flap actuator motor (temperature control)

 Air distribution air ducting flap via central air distribution actuator motor (blower regulation)

Vehicles with CODE 581 (Automatic air conditioning):

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

 Left blend air flap via left blend air flap actuator motor (left temperature control)

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

 Air distribution air ducting flap via central air distribution actuator motor (blower regulation)

 The position of the air distribution air ducting flap is recorded by the central air distribution position detection microswitch. The status of the microswitch is read in by the automatic air conditioning control and operating unit. If an incorrect position is detected, the position of the air ducting flap is readjusted by the automatic air conditioning control and operating unit via the central air distribution actuator motor.

 Model 117 as of 6/1/13, 156 as of 6/1/13, 176 as of 6/1/13, 242 as of 6/1/13, 246 as of 6/1/13
The fresh air/recirculated air flap is closed after an accident (crash signal sent).

 In order to prevent fogging of windows, the air distribution air duct flap is closed t = 2 min after switching off circuit 15. With the "Engine running" or "Drivetrain operational" signal, the air distribution air duct flap remains in this fixed position for an additional t = 30 s (approx.). After that, all adjustments are possible 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 %. This achieves a significant reduction in the door closing forces. The function can be set with the diagnostic tester.

P83.10-2803-75

Function sequence for actuation of refrigerant compressor (except model 242.890)

The refrigerant compressor is responsible for induction and compression of the refrigerant. The refrigerant compressor output is continuously regulated up to 100 % through the refrigerant compressor closed-loop control valve by the automatic air conditioning control and operating unit. The automatic air conditioning control and operating unit actuates the refrigerant compressor regulating valve directly.

On vehicles 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 actuates the refrigerant compressor magnetic clutch directly.

The automatic air conditioning control and operating unit also transmits the idle speed increase request via the interior CAN, the electronic ignition lock control unit and the chassis CAN (variant 1) or chassis CAN 1 (variant 2) to the ME-SFI [ME] control unit (engine 270 and 133) or the CDI control unit (engine 651).

With engine 607, the automatic air conditioning control and operating unit transmits the idle speed increase request via the interior CAN, the electronic ignition lock control unit, the chassis CAN (variant 1) or chassis CAN 1 (variant 2), the powertrain control unit and the drivetrain CAN to the CDI control unit.

The CDI control unit or the ME-SFI [ME] control unit 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.

 Model 117 as of 6/1/13, 156 as of 6/1/13, 176 as of 6/1/13, 242 as of 6/1/13, 246 as of 6/1/13
The refrigerant compressor is switched off via the refrigerant compressor regulating valve (except CODE B09 (Refrigerant compressor with magnetic clutch)) or via the refrigerant compressor magnetic clutch (with CODE B09 (Refrigerant compressor with magnetic clutch)) after an accident (crash signal transmitted).

Function sequence for actuation of electric refrigerant compressor (model 242.890)

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 the climate control LIN.

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

 The electric refrigerant compressor is switched off after an accident (crash signal transmitted).

Function sequence for fan motor actuation

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 transmits the request via the interior CAN, the electronic ignition lock control unit and the chassis CAN (variant 1) or chassis CAN 1 (variant 2) to the ME-SFI [ME] control unit (engine 270 and 133) or the CDI control unit (engine 651).

With engine 607, the automatic air conditioning control and operating unit transmits the request via the interior CAN, the electronic ignition lock control unit, the chassis CAN (variant 1) or chassis CAN 1 (variant 2), the powertrain control unit and the drivetrain CAN to the CDI control unit.

In model 242.890, the automatic air conditioning control and operating unit transmits the request via the interior CAN, the electronic ignition lock control unit and the chassis CAN (variant 1) or chassis CAN 1 (variant 2) to the powertrain control unit.

The ME-SFI [ME] control unit (engine 270 and engine 133) or the CDI control unit (engine 651 and engine 607) or the powertrain control unit (model 242.890) then calculates the specified fan speed depending on the engine temperature, compares this with the request from the automatic air conditioning control and operating unit and then actuates the fan motor accordingly.

Function sequence for actuation of the coolant circulation pump (with CODE 581 (Automatic air conditioning) and except CODE 494 (USA version))

In vehicles with internal combustion engines, the coolant circulation pump is used to support the coolant circuit, e.g. at low engine rpm or when the residual heat utilization function is being used.

On model 242.890, the coolant circulation pump is only used to circulate the coolant.

The coolant circulation pump is actuated directly by the automatic air conditioning control and operating unit.

Function sequence for actuation of heater circuit circulation pump (model 242.890)

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 actuated by the automatic air conditioning control and operating unit via the climate control LIN.

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

The PTC heater booster is actuated by the automatic air conditioning control and operating unit via the climate control LIN as and when needed.

 Model 117 as of 6/1/13, 156 as of 6/1/13, 176 as of 6/1/13, 246 as of 6/1/13
The PTC heater booster is switched off in the event of an accident (crash signal transmitted).

Function sequence for actuation of the front evaporator shutoff valve (model 242.890)

The front evaporator shutoff valve is used to control the flow of refrigerant to the 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 high-voltage battery cooling system shutoff valve (model 242.890)

The high-voltage battery cooling system shutoff valve is used to regulate the flow of refrigerant into the heat exchanger. When the refrigerant flows through the heat exchanger, thermal energy is extracted from the coolant of the high-voltage battery cooling circuit and overheating is thus prevented. The thermal management control unit transmits the relevant request via the electric drive CAN, the gateway powertrain control unit, the vehicle CAN, the powertrain control unit, the chassis CAN (variant 1) or chassis CAN 1 (variant 2), the electronic ignition lock control unit and the interior CAN to the automatic air conditioning control and operating unit.

The automatic air conditioning control and operating unit sends feedback the opposite way to the powertrain control unit. The powertrain control unit actuates the high-voltage battery cooling shutoff valve directly.

Function sequence for actuation of the high voltage PTC heater (model 242.890)

The high-voltage PTC heater heats up the coolant in the heater circuit and is activated as required by the automatic air conditioning control and operating unit via the climate control LIN. 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.

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

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 panoramic roof (with CODE 413 (Panoramic sliding sunroof)) are closed. If the air recirculation mode button is then operated for t > 1.5 s, the side windows and the panoramic roof (with CODE 413 (Panoramic sliding sunroof)) are moved to their default positions (insofar as they were not manually adjusted during the air recirculation mode).

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

 Refrigerant compressor switched on (except CODE B09 (Refrigerant compressor with magnetic clutch))

 Refrigerant compressor with magnetic clutch switched on (with CODE B09 (Refrigerant compressor with magnetic clutch))

 Electric refrigerant compressor switched on (model 242.890)

 Defrost mode not active

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

The air quality sensor records the pollutant levels of the outside air. The automatic air conditioning control and operating unit reads in the signals of the air quality sensor via the climate control LIN. As of a certain pollutant concentration, the fresh air/recirculated air flap is automatically set to the recirculated air position by the fresh air/recirculated air flap actuator motor. 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. Following this, operation continues first with 80 % pollutant-controlled recirculated air and after another t = 10 s, as required, with 100 % pollutant-controlled recirculated air. The pollutant-controlled air recirculation mode is not indicated by the LED in the air recirculation mode button.

Function sequence for defroster function

By pressing the defrosting button (except model 242.890) or the heated windshield defrost button (model 242.890), all air flaps apart from the air distribution air duct flap and the fresh air/recirculated air flap are closed. These are fully opened. The LED in the respective button lights up as function feedback. The air distribution air duct flap is 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 blower motor is actuated by the automatic air conditioning control and operating unit via the blower regulator in such a way that the best possible defrost mode is provided, depending on the temperature of the air flowing out. 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. In model 242.890 with CODE 597 (Heated windshield), the heated windshield is also actuated.

 Model 117, 156, 176, 242, 246
with code 580 (Air-conditioning system)
The warm air supply is controlled by actuation of the left blend air flap actuator motor for both the driver and the front passenger.

 Model 117, 156, 176, 242, 246
with code 581 (Automatic air conditioning)
The warm air supply is controlled by actuation of the left blend air flap actuator motor for the driver and by actuation of the right blend air flap actuator motor for the front passenger.

Additional function requirements for evaporator drying process

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

 Evaporator temperature T > 3 °C

 Outside temperature T > 20 °C

 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. With "Engine OFF", the timer is activated in the instrument cluster.

Vehicles with variant 1 networking:

The CDI control unit (engine 651) or the ME-SFI [ME] control unit (engine 270 and 133) transmits the "engine running" signal via the chassis CAN to the instrument cluster.

With engine 607, the CDI control unit sends the "Engine running" signal via the drivetrain CAN, the powertrain control unit and the chassis CAN to the instrument cluster.

On model 242.890, the powertrain control unit sends the "Drivetrain operational" signal via the chassis CAN to the instrument cluster.

Vehicles with variant 2 networking:

The CDI control unit (engine 651) or the ME-SFI [ME] control unit (engine 270 and 133) transmits the "engine running" signal via chassis CAN 1, the electronic ignition lock control unit and chassis CAN 2 to the instrument cluster.

With engine 607, the CDI control unit transmits the "engine running" signal via the drivetrain CAN, the powertrain control unit and chassis CAN 1, the electronic ignition lock control unit and chassis CAN 2 to the instrument cluster.

In model 242.890, the powertrain control unit transmits the "drivetrain operational" signal via chassis CAN 1, the electronic ignition lock control unit and chassis CAN 2 to the instrument cluster.

After a waiting time of t = 1 h the instrument cluster transmits the request for evaporator drying via the interior CAN to the automatic air conditioning control and operating unit, which starts evaporator drying. To this end, the blower is activated at the lowest setting for t = 30 min.

The automatic air conditioning control and operating unit sends the "Blower ON" request via climate control LIN to the blower regulator. The blower regulator actuates the blower motor at the slowest speed.

Function sequence for residual heat utilization (with CODE 581 (Automatic air conditioning) and except CODE 494 (USA version))

Pressing the "REST" button on the automatic air conditioning control and operating unit switches on the residual heat utilization function.

Except model 242.890:

The automatic air conditioning control and operating unit actuates the coolant circulation pump directly. The coolant circulation pump delivers the still warm (residual heat) coolant through the heat exchanger.

Model 242.890:

The automatic air conditioning control and operating unit actuates the heater circuit circulation pump via the climate control LIN if the coolant temperature is sufficient. The heater circuit circulation pump delivers the still warm coolant (residual heat) through the heater heat exchanger.

At the same time, the automatic air conditioning control and operating unit actuates the blower regulator via climate control LIN, which then actuates the blower motor at low speed. 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 the air conditioning system after an accident (crash signal transmitted) as of 01.06.2013

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 motor is 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 control valve is switched off. 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 (model 242.890) is no longer energized.

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

 The high-voltage PTC heater (on model 242.890) is switched off.

The supplemental restraint system control unit transmits the crash signal via the chassis CAN (variant 1) or chassis CAN 1 (variant 2), the electronic ignition lock control unit and the interior CAN to the automatic air conditioning control and operating unit.

 Detailed information concerning the actuation of the individual air conditioning system components is available within this document in the "Function sequence for 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 increased to 100 %, the temperature is set to "maximum cold", and air recirculation mode is switched on.