GF83.40-P-2004CW Regulation of Automatic Air Conditioning, Function

GF83.40-P-2004CW Regulation Of Automatic Air Conditioning, Function

Function requirements
^ Circuit 15 On
^ Circuit 15 On
^ Circuit 61 ON (for cooling operation)
^ Refrigerant compressor (A9) switched on (for cooling operation)

The status of circuit 15 is transmitted to the interior CAN by the electronic ignition lock control unit (N73).
The status of circuit 61 is transmitted by the CDI control unit (N3/9) (with diesel engines) or the ME-SFI [ME] control unit (N3/10) (with gasoline engines) to the front SAM control unit with fuse and relay module (N10/1) via the chassis CAN. This routes the message on the interior CAN. The automatic air conditioning control and operating unit (N22/7) picks up the respective message.

Control function sequence, general
Electronic control of the temperature and the air distribution in the interior takes place depending on the settings selected at the control and operating unit and the marginal conditions recorded via various sensors (e.g. interior temperature, outside temperature, coolant temperature, vehicle speed).
The determination of these variables is described after the control related settings.

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

Control-related settings
^ Automatic control
^ Manual control
^ Defrost function
^ Maximum cooling output (only United States of America)
^ Refrigerant compressor switched on or off

Automatic control
Function requirements:
^ Auto button pressed (LED illuminates)

Function sequence, automatic control
The temperature, the air distribution and the air volume are controlled depending on the temperature preselection at the control and operating unit and the marginal conditions that exist at the time.

The following factors are taken into consideration by the control and operating unit:
^ Interior temperature
^ Outside temperature
^ Dew point temperature (outside air humidity)
with code (581) Comfort automatic air conditioning)
^ Coolant temperature
^ Temperature at air outlets in vehicle
^ Solar radiation on the vehicle
^ Vehicle speed
^ Temperature at the evaporator
^ Refrigerant pressure
^ Engine speed

The air is cooled by means of controlled actuation of the refrigerant compressor. Heating takes place by mixing it with air heated by the heat exchanger via the blend air flaps.

In vehicles with diesel engine the PTC heater booster (R22/3) is also activated if necessary. The blower motor (A32m1) is actuated by the control and operating unit via the blower regulator (A32n1). The following components are available for actuating the air flaps for air distribution:

Vehicles with code (581) Comfort automatic air conditioning
^ Fresh air/recirculated air flap actuator motor (M2/5)
^ Left blend air flap actuator (M2/6)
^ Right blend air flap actuator (M2/7)
^ Left defroster vent flap actuator motor (M2/8)
^ Right defroster vent flap actuator motor (M2/9)
^ Left footwell flap actuator motor (M2/10)
^ Right footwell flap actuator motor (M2/11)
^ Left center outlet flap actuator motor (M2/12)
^ Right center outlet flap actuator motor (M2/13)
^ Diffuser flap actuator motor (M2/21)
^ Ram air flap actuator motor (M2/34)
^ Rear blend air flap actuator motor (M2/35)

Vehicles without code (581) Comfort automatic air conditioning
^ Fresh air/air recirculation flap actuator motor
^ Left blend air flap actuator
^ Left blend air flap actuator
^ Defroster vent flap actuator motor (M2/16)
^ Air distribution flap actuator motor (M16/22)

Manual control

Function requirements:
^ Air distribution and air volume manually modified (LED in Auto button not illuminated)

Function sequence, manual control
The temperature, the air distribution and the air volume are controlled depending on the settings made at the control and operating unit.
The driver side temperature preselection can be taken over for the other zones by pressing the Mono button (not United States of America).

In vehicles with code (581) Comfort automatic air conditioning, the current driver side air distribution setting is taken over for the front passenger side.

Defrost function

Function requirements:
^ Defrost button pressed (LED illuminates)

Function sequence, defrost function
Activating the function causes the previous settings to be overlaid. The air is dried (cooled) and then heated to the maximum level. The blower motor is actuated at full power (depending on the coolant temperature).

The defroster flaps are set so that the maximum air flow is directed at the windshield and the front side windows.

Maximum cooling output
The basic ventilation level is increased to 100% by pressing the MAX A/C button.

Refrigerant compressor switched on or off
Pressing the A/C button deactivates the actuation of the refrigerant compressor. The other functionalities of the automatic air conditioning are still available. However, cooling to a temperature that is less than the current outside temperature is not possible.

Determining the variables for controlling the automatic air conditioning:
^ Interior temperature
The interior temperature is recorded by the interior temperature sensor (B10/4) in the vicinity of the instrument panel. This is discretely read in by the control and operating unit. The interior temperature is recorded in the vicinity of the roof by the interior temperature sensor (N70b1) (with code (414) Power glass tilting/sliding sunroof) or by the interior temperature sensor (N70/3b1) (without code (414) Power glass tilting/sliding sunroof).

With code (414) Power glass tilting/sliding sunroof the value of the interior temperature sensor is transmitted by the overhead control panel control unit (N70) via the interior CAN. Without code (414) Power glass tilting/sliding sunroof, the value of the interior temperature sensor is discretely read in by the control and operating unit.

^ Outside temperature
The outside temperature sensor (B14) measures the outside temperature. The temperature value is read in by the front SAM control unit and transmitted to the control and operating unit via the interior CAN. The control and operating unit needs this value to attain the required interior temperature by making appropriate adjustments to the blend air flaps. If the vehicle is stationary, the measured temperature may differ considerably from the outside temperature. The outside temperature is only used for control if the vehicle speed is v > 20 km/h.

^ Dew point temperature
(with code (581) Comfort automatic air conditioning) The dew point is measured by the dew point sensor (B11/12). The dew point is needed to control the refrigerant compressor. The dew point sensor is read in by the control and operating unit via the climate control LIN and transmitted via the interior CAN.

^ Coolant temperature
The temperature of the coolant is recorded by the coolant temperature sensor (B11/4). This is read in by the CDI control unit or the ME-SFI [ME] control unit and transmitted to the front SAM control unit via the chassis CAN. This transmits the value to the control and operating unit via the interior CAN. This value is used to control the blend air flaps, control the PTC heater booster and actuate the coolant circulation pump (M13/5).

^ Temperature at air outlets in the vehicle
The temperature at the air outlets is recorded by the left side vent temperature sensor (B10/31), the right side vent temperature sensor (B10/32), the left front footwell vent temperature sensor (B10/35) and the right front footwell vent temperature sensor (B10/36). The control and operating unit controls the outlet air temperatures of the respective air outlets. The temperature sensors are discretely read in by the control and operating unit.

With code (581) Comfort automatic air conditioning, the rear footwell vent temperature sensor (B10/38) is also installed at the rear air outlet.

^ Solar radiation on the vehicle
The control and operating unit uses the sun sensor (B32/3) to record the angle of incidence of solar radiation on the vehicle. The interior temperature and blower speed are adapted according to the intensity. In the event of one-sided solar radiation, an appropriate temperature difference is set between the right and the left temperature control setpoints. The sun sensor is read in by the control and operating unit via the climate control LIN.

^ Vehicle speed
The vehicle speed is transmitted by the instrument cluster (A1) to the control and operating unit via the interior CAN. The vehicle speed is used to control the ram air function and for internal outside temperature calculations e.g. during stationary operation.

^ Temperature at evaporator
In order to prevent the evaporator from icing up, the temperature at the evaporator is recorded by the evaporator temperature sensor (B10/6). The evaporator temperature sensor is directly read in by the control and operating unit.

^ Refrigerant pressure
The pressure of the refrigerant is recorded by the refrigerant pressure sensor (B12). The refrigerant pressure sensor is read in discretely by the front SAM control unit and relayed to the control and operating unit via the interior CAN. The pressure is compared with a stored temperature pressure curve. The refrigerant pressure sensor operates within a pressure range of p = 0 to 35 bar. At a refrigerant pressure of p < 1.7 bar and p > 30 bar the refrigerant compressor is shut off.

^ Engine speed
The engine speed is recorded by the CDI control unit or the ME-SFI [ME] control unit and transmitted to the front SAM control unit via the chassis CAN. Among other things, the engine speed is used to control the refrigerant compressor.