Regulation of Automatic air conditioning, function

Function requirements, general

 Circuit 15 On

 Automatic air conditioning switched on

 Climate control circuit 61 ON (for cooling mode)

 Refrigerant compressor (A9) switched on (for cooling mode)

Automatic air conditioning regulation, general

The electronic regulation of the temperature and the air distribution in the vehicle interior takes place depending on the settings selected on the AAC [KLA] control and operating unit (N22) (without code (581) Comfort automatic air conditioning) or on the comfort AAC [KLA] control and operating unit (N22/7) (with code (581) Comfort automatic air conditioning) and the variables measured by various sensors (e.g. outside temperature, interior temperature, coolant temperature).

------------------------------------------------------------------------------------------

The control and operating unit is networked via the interior CAN and the AC bus 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.

The automatic air conditioning regulation comprises the following subfunctions:

 Function sequence, adjustments that are relevant for regulation

 Function sequence, determining variables

 AC component actuation function sequence

------------------------------------------------------------------------------------------

Function sequence, adjustments that are relevant for regulation

The function sequence for adjustments that are relevant for regulation comprises the following subfunctions:

 Function sequence for automatic regulation

 Function sequence with manual regulation

 Function sequence of defroster function

Additional function requirements, automatic regulation

 AUTO button pressed (LED lights up)

Function sequence for automatic regulation

The regulation of temperature, air distribution, and air volume takes place depending on the temperature preselection on the control and operating unit and the currently existing basic conditions. The air distribution and air volume are set automatically.

------------------------------------------------------------------------------------------

In the process, the control and operating unit takes the following variables into account:

- Ambient temperature

- Interior temperature

- Coolant temperature

- Solar radiation onto the vehicle
(with code (581) Comfort automatic air conditioning)

- Vehicle speed

- Temperature on evaporator

- Refrigerant pressure

- Engine speed

- Pollutant concentration of the outside air
(with code (581) Comfort automatic air conditioning)

- Dew point temperature (air humidity of the outside air)
(with code (581) Comfort automatic air conditioning)

- Door status

- Window position and panoramic roof position (with code (413) Panoramic glass sunroof with top sliding roof)

------------------------------------------------------------------------------------------

Additional function requirements, manual regulation

 Air distribution and air volume changed manually
(LED in AUTO button does not light up)

Function sequence with manual regulation

The regulation of temperature, air distribution, and air volume takes place depending on the temperature selections made on the control and operating unit and the currently existing basic conditions.

In the process, the control and operating unit takes the following variables into account:

- Ambient temperature

- Interior temperature

- Coolant temperature

- Solar radiation onto the vehicle
(with code (581) Comfort automatic air conditioning)

- Vehicle speed

- Temperature on evaporator

- Refrigerant pressure

- Engine speed

------------------------------------------------------------------------------------------

- Pollutant concentration of the outside air
(with code (581) Comfort automatic air conditioning)

- Dew point temperature (air humidity of the outside air)
(with code (581) Comfort automatic air conditioning)

- Door status

- Window position and panoramic roof position (with code (413) Panoramic glass sunroof with top sliding roof)

Additional function requirements, defroster function

 Defroster button pressed (light emitting diode lights up)

Function sequence of defroster function

When the defroster button is pressed, all air flaps are closed with the exception of the defroster flaps and the fresh air/air recirculation flap. These are fully opened.

The defroster and side air vents are adjusted so that the maximum air flow is directed to the windshield and the front side windows.

------------------------------------------------------------------------------------------

The blower motor (A32m1) is actuated by the control and operating unit via the blower regulator (A32n1) to ensure the best possible defrost mode in accordance with the temperature of the outflowing air.

The refrigerant compressor is also switched on to dry the outflowing air. The air is dried (cooled) and then heated up to the maximum temperature.

 Defrost mode takes place in vehicles with code (581) Comfort automatic air conditioning by actuating the left defroster vent flap actuator motor (M2/8) and the right defroster vent flap actuator motor (M2/9) separately for the driver and front passenger sides. In vehicles without code (581) Comfort automatic air conditioning the left and right defroster vent flap actuator motor (M2/16) is actuated. Defrost mode therefore takes place for the driver side and the front passenger side together.

------------------------------------------------------------------------------------------

Function sequence, determining variables

The variables are determined using the following subfunctions:

 Function sequence, determining the outside temperature

 Function sequence, determining the interior temperature

 Function sequence, determining the coolant temperature

 Function sequence, determining the vehicle speed

 Function sequence for determining the level of solar radiation onto the vehicle (with code (581) Comfort automatic air conditioning)

 Function sequence for determining the temperature at the evaporator

 Function sequence, determining the refrigerant pressure

 Function sequence, determining the engine speed

 Function sequence for determining the pollutant concentration of the outside air (with code (581) Comfort automatic air conditioning)

 Function sequence for determining dew point temperature
(with code (581) Comfort automatic air conditioning)

 Function sequence, determining the door status

 Function sequence, determining the window position and the panoramic roof position (with code (413) Panoramic glass sunroof with top sliding sunroof)

------------------------------------------------------------------------------------------

Function sequence, determining the outside temperature

The outside temperature indicator temperature sensor (B14) records the outside temperature. The temperature value is read in directly by the front SAM control unit with fuse and relay module (N10/1) and transmitted via the interior CAN to the control and operating unit.

Function sequence, determining the interior temperature

The interior temperature is recorded in the vicinity of the instrument panel by the in-car temperature sensor (N22b1) (without code (581) Comfort automatic air conditioning) or the in-car temperature sensor (N22/7b1) (with code (581) Comfort automatic air conditioning) in the control and operating unit and in the front area of the roof by the in-car temperature sensor (N70b1) in the overhead control panel control unit (N70).

The overhead control panel control unit reads in the values from the in-car temperature sensor directly and transmits them to the control and operating unit via the interior CAN.

------------------------------------------------------------------------------------------

The relevant in-car temperature sensor is equipped with an aspirator blower which draws in air out of the vehicle interior. The aspirator blower ensures that the vehicle interior air is constantly circulated at the in-car temperature sensor and therefore ensures a high degree of control accuracy.

By means of the in-car temperature sensor, temperature control is achieved that is largely independent of the air flow conditions in the vehicle interior.

Function sequence, determining the coolant temperature

The temperature of the coolant is measured by the coolant temperature sensor (B11/4). The temperature value is read in by the CDI control unit (N3/9) (for diesel engines) or by the ME-SFI [ME] control unit (N3/10) (for gasoline engines) and transmitted to the EIS [EZS] control unit (N73) via engine compartment CAN. It transmits the value to the control and operating unit via interior CAN.
This value is used to control the blend air flaps and to actuate the heater circulation pump (M13).

------------------------------------------------------------------------------------------

Function sequence, determining the vehicle speed

The vehicle speed is transmitted by the instrument cluster (A1) to the control and operating unit via interior CAN. The vehicle speed is used for the internal calculation of the outside temperature, e.g. during operation while standing.

Function sequence for determining the level of solar radiation onto the vehicle (with code (581) Comfort automatic air conditioning)

The angle of incidence and intensity of the solar radiation on the vehicle are recorded by the C-AAC sun sensor (4 in total) (B32/2). The control and operating unit reads in the signals from the sun sensor via the AC bus and adapts the interior temperature and the blower speed accordingly.

In the event of one-sided solar radiation, an adequate temperature difference is set between the left and the right regulated specified temperatures.

------------------------------------------------------------------------------------------

Function sequence, determining the temperature at the evaporator

The evaporator temperature is recorded by the evaporator temperature sensor (B10/6). The control and operating unit reads in the

signals of the evaporator temperature sensor directly.

If the evaporator temperature falls to approx. T = 2 °C, the refrigerant compressor is switched off in order to prevent the evaporator from icing up.

Function sequence, determining the refrigerant pressure

The refrigerant pressure is registered by the refrigerant pressure sensor (B12). The pressure is compared to a stored temperature-pressure curve.
At a refrigerant pressure of p < 1.75 and p > 30 bar, the refrigerant compressor is switched off.

The signals of the refrigerant pressure sensor are read in by the front SAM control unit directly and transmitted to the control and operating unit via the interior CAN.

------------------------------------------------------------------------------------------

Function sequence, determining the engine speed

The engine speed is registered by the CDI control unit or the ME-SFI [ME] control unit and transmitted to the EIS [EZS] control unit via engine compartment CAN. This relays the value to the control and operating unit via the interior CAN.
The engine speed is used among others to regulate the refrigerant compressor.

Function sequence for determining the pollutant concentration of the outside air (with code (581) Comfort automatic air conditioning)

The comfort automatic air conditioning multifunction sensor (B31) records the concentration of carbon monoxide (CO) and nitrogen oxide (NOX) pollutants in the outside air. The data from the multifunction sensor is read in directly by the control and operating unit via the AC bus. The control and operating unit controls the automatic recirculation according to the read in values.

------------------------------------------------------------------------------------------

Function sequence, determining the dew point temperature

(with code (581) Comfort automatic air conditioning)

The C-AAC multifunction sensor uses the ambient temperature and air humidity to calculate the dew point temperature and transmits this data via the AC bus to the control and operating unit.The dew point temperature is needed to regulate the refrigerant compressor.

Function sequence, determining the door status

The left front door contact switch (S17/3) and the right front door contact switch (S17/4) record the open/closed status of the respective doors. The door status is read in directly by the rear SAM control unit with fuse and relay module (N10/2) and transmitted via the interior CAN to the control and operating unit.

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

------------------------------------------------------------------------------------------

Function sequence, determining the window position and the panoramic roof position (with code (413) Panoramic glass sunroof with top sliding sunroof)

The relevant window position is read in by the left front door control unit (N69/1) and the right front door control unit (N69/2) and transmitted to the control and operating unit.

The panoramic roof position is read in by the overhead control panel control unit and transmitted to the control and operating unit.

AC component actuation function sequence

The AC component actuation function sequence comprises the following subfunctions:

 Function sequence, actuation of the refrigerant compressor

 Function sequence, actuation of blower motor

 Function sequence, actuation of the air ducting flaps

 Function sequence for actuation of engine and air conditioning electric suction fan with integrated control (M4/7)

------------------------------------------------------------------------------------------

Function sequence, actuation of the refrigerant compressor

The refrigerant compressor is responsible for induction and compression of the refrigerant. The refrigerant compressor output is regulated continuously up to 100 % by the control and operating unit via the compressor control valve.

The control and operating unit transmits the switch-on request via the interior CAN to the front SAM control unit. This receives the request and actuates the compressor control valve.

Function sequence, actuation of blower motor

Ventilation is achieved with the aid of the blower motor. The control and operating unit transmits an actuation of 0 to 100 % to the blower regulator via the AC bus. Depending on the control voltage, the blower regulator regulates the operating voltage for the blower motor from U = 0 V up to U = 12 V and thus the rotational speed of the blower motor from 0 up to 100 %.

------------------------------------------------------------------------------------------

The actuation (operating voltage) of the blower motor is influenced by the following factors:

- Blower selector wheel setting (MANUAL/AUTO)

- Operating functions

- Mode (heating/cooling)

- Coolant temperature

- Vehicle speed

- Solar radiation
(with code (581) Comfort automatic air conditioning)

- Fresh air/air recirculation flap position

- Flap positions

- Circuit 15 (blower ON), circuit 50 (starter running, blower off)

Air ducting flaps actuation function sequence

The air distribution in the vehicle interior is controlled by corresponding adjustment of the air duct flaps in the air conditioning housing.

The control and operating unit then actuates the following components via the AC bus accordingly.

------------------------------------------------------------------------------------------

Vehicles without code (581) Comfort automatic air conditioning:

- For fresh air/recirculated air control:

- Fresh air/air recirculation flap actuator motor (M2/5)

- for temperature control:

- Left blend air flap actuator motor (M2/6)

- Right blend air flap actuator motor (M2/7)

- for ventilation control:

- Left and right footwell flaps actuator motor (M2/15)

- Left and right defroster flaps actuator motor

- Air flaps actuator motor (M2/21)

Vehicles with code (581) Comfort automatic air conditioning:

- For fresh air/recirculated air control:

- Fresh air/air recirculation flap actuator motor

- Activated charcoal filter flap adjustment motor (A32m2)

- for temperature control:

- Left blend air flap actuator motor

- Right blend air flap actuator motor

------------------------------------------------------------------------------------------

- for ventilation control:

- Left defroster flap actuator motor

- Right defroster flap actuator motor

- Left footwell flap actuator motor (M2/10)

- Right footwell flap actuator motor (M2/11)

- Left air flap actuator motor (M2/19)

- Right air flap actuator motor (M2/20)

Function sequence, actuation of engine and air conditioning electric suction fan with integrated control

The electric suction fan serves to cool the coolant and refrigerant.
The control and operating unit calculates the specified fan speed depending on the refrigerant pressure and transmits the request to the EIS [EZS] control unit via interior CAN. This transmits the request to the CDI control unit or the ME-SFI [ME] control unit via engine compartment CAN. The CDI control unit or the ME-SFI [ME] control unit then calculates the target blower speed depending on the engine temperature and compares it with the air conditioning request. It then actuates the electric suction fan accordingly.