Regulation of Automatic Air Conditioning, Function

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

^ Circuit 15
^ Automatic air conditioning switched on
^ Circuit 61 (for cooling mode)
^ Refrigerant compressor (A9) switched on (for cooling mode)

Control, general
The electronic regulation of the temperature and the air distribution in the interior takes place depending on the settings selected on the AAC [KLA] control and operating unit (N22) and the variables registered by the various sensors (e.g. interior temperature, outside temperature, coolant temperature and vehicle speed).

The determination of these variables is described following the description of the adjustments that are relevant for regulation. 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 comes on)

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 on the vehicle
- Vehicle speed
- Temperature on evaporator
- Refrigerant pressure
- Engine speed
- Pollutant concentration of outside air
- Dew point temperature (air humidity of outside air)
- Door status
- Window position
- Vario roof status

Additional function requirements, manual regulation
^ Air distribution or air volume changed manually (LED in AUTO button is not on)

Function sequence with manual regulation
The temperature, the air distribution and the air volume are controlled depending on the settings made at the control and operating unit and the AAC [KLA] center and side vent control system (N18/2) and the general conditions that currently exist.

The center and side air vent control system relays the settings discretely to the control and operating unit.

In the process, the control and operating unit takes the following variables and settings into account:
- Center and side air vent control system
- Ambient temperature
- Interior temperature
- Coolant temperature
- Solar radiation on the vehicle
- Vehicle speed
- Temperature on evaporator
- Refrigerant pressure
- Engine speed
- Pollutant concentration of outside air
- Dew point temperature (air humidity of outside air)
- Door status
- Window position
- Vario roof status

Additional function requirements, defroster function
^ Defrost button pressed (LED is on)

Function sequence of defroster function
When the defroster button is pressed, all air flaps are closed with the exception of the defroster vent flaps and the fresh air/air recirculation flap. These are fully opened.
The defroster vent flaps are adjusted so that the maximum air flow is directed to the windshield and the front side windows. The blend air flaps are set to full warm air supply.

The blower motor (A32m1) is actuated by the control and operating unit via the blower regulator (A32n1) to ensure the best possible defrost mode dependent 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 (cooled) and then heated up to the maximum temperature.

Defrosting is carried out by the left defroster vent flap actuator motor (M16/13) for the driver and the right defroster vent flap actuator motor (M16/14) for the front passenger.

Function sequence, determining variables
The function sequence for determining variables comprises 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 solar radiation on the vehicle
^ Function sequence, determining the vehicle speed
^ Function sequence, determining the temperature at the evaporator
^ Function sequence, determining the refrigerant pressure
^ Function sequence, determining the engine speed
^ Function sequence, determining the pollutant concentration of the outside air
^ Function sequence, determining the dew point temperature
^ Function sequence, determining the door status
^ Function sequence, determining the window position
^ Function sequence, determining the Vario roof status

Function sequence, determining the outside temperature
The outside temperature indicator temperature sensor (B14) measures the outside temperature. The temperature value is read in directly by the driver-side SAM control unit (N10/10) and transmitted to the control and operating unit via the interior CAN.

The control and operating unit needs 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.

Function sequence, determining the interior temperature
The interior temperature is registered in the instrument panel area by the in-car temperature sensor (N22b1) and directly read in by the control and operating unit.
The interior temperature is registered in the roof area by the in-car temperature sensor (N70b1) and read in by the overhead control panel control unit (N70).It transmits the value to the control and operating unit via interior CAN.

The in-car temperature sensors are not evaluated if the Vario roof is open.

Each of the two in-car temperature sensors is equipped with a ventilation blower that draws in the air that is required for measuring the temperature in the vehicle interior.
A mean value is calculated from the in-car temperature sensor measurements. Together with the value from the outside temperature indicator temperature sensor, the mean value is compared with a performance map that is stored in the control and operating unit and used to control the interior temperature.

Under the following conditions the mean in-car temperature value is retained by the control and operating unit and ensures that the air conditioning system continues to operate with the specified temperature:
- Side window open
- Door open

Function sequence, determining the coolant temperature
The temperature of the coolant is registered by the coolant temperature sensor (B11/4). The temperature value is read in by the ME-SFI [ME] control unit (N3/10) and transmitted to the EIS [EZS] control unit (N73) via the 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 solar radiation on the vehicle
The control and operating unit registers the angle of incidence and the intensity of the solar radiation on the vehicle via the AC bus using the AAC [KLA] sun sensor (4 in total) (B32/2). The interior temperature and the blower speed are adjusted in accordance with the measurements.
In the event of one-sided solar radiation, an appropriate temperature difference is set between the right and left specified control temperatures.

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, determining the temperature at the evaporator
In order to prevent the evaporator from icing up, the temperature at the evaporator is registered by the evaporator temperature sensor (B10/6) and directly read in by the control and operating unit. If the evaporator temperature drops to approx. T = 2 °C, the refrigerant compressor is switched off.

Function sequence, determining the refrigerant pressure
The refrigerant pressure is registered by the refrigerant pressure sensor (B12). The pressure is compared with a stored temperature/ pressure curve. At a refrigerant pressure of p < 1.75 bar or p > 30 bar the refrigerant compressor is switched off. The refrigerant pressure sensor is read in directly by the driver-side SAM control unit and relayed to the control and operating unit via the interior CAN.

Function sequence, determining the engine speed
The engine speed is registered by the ME-SFI [ME] control unit and transmitted to the EIS [EZS] control unit via the engine compartment CAN. It transmits the value to the control and operating unit via interior CAN.

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

Function sequence, determining the pollutant concentration of the outside air
The AAC [KLA] multifunction sensor (B31/1) registers the concentration of the pollutants carbon monoxide (CO) and nitrogen oxide (NO X).
The values are read in 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
The AAC [KLA] multifunction sensor calculates the dew point from the ambient temperature and the air humidity, and transmits it to the control and operating unit via the AC bus. The dew point is needed to regulate the refrigerant compressor.

Function sequence, determining the door status
The open and closed status of the respective doors is registered by the left door contact switch (S17/3) and the right door contact switch (S17/4). The door status is read in by the rear SAM control unit (N10/8) and transmitted 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
The window position is read in by the left door control unit (N69/1) and the right door control unit (N69/2) and transmitted to the control and operating unit.

Function sequence, determining the Vario roof status
The RSC [UVS] control unit (N52) transmits the status of the Vario roof to the control and operating unit via the interior CAN.

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, 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 from 0 to 100 % by the control and operating unit via the compressor control valve.

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

Function sequence, actuation of blower motor
Ventilation is provided with the aid of the blower motor. The control and operating unit transmits a signal from 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 output 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
- Air distribution
- AC button
- Residual engine heat utilization system
- Mode: heating or cooling
- Coolant temperature
- Vehicle speed
- Vario roof open or closed
- Solar radiation
- Fresh air/air recirculation flap position
- Flap positions
- Status of circuit 15 and circuit 50

The blower output can be increased to match the outside temperature. To keep the inside temperature constant and the windows clear at low temperatures, the blower output is increased by 15 % at outside temperatures of T = -10 °C to -15 °C.

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 conditioner housing.
The following components are actuated by the control and operating unit via the AC bus:
- For fresh air/recirculated air control:
- Fresh air and air recirculation flap actuator motor (M16/21)
- for temperature control:
- Left blend air flap actuator motor (M16/28)
- Right blend air flap actuator motor (M16/29)
- for ventilation control:
- Left defroster vent flap actuator motor
- Right defroster vent flap actuator motor
- Left footwell flap actuator motor (M16/15)
- Right footwell flap actuator motor (M16/16)
- Left center air flap actuator motor (M16/23)
- Right center air flap actuator motor (M16/24)
- Air flap actuator motor, left side vent (M16/25)
- Air flap actuator motor, right side vent (M16/26)

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 ME-SFI [ME] control unit via the engine compartment CAN. The ME-SFI [ME] control unit calculates the specified fan speed depending on the engine temperature, compares it to the air conditioning request and actuates the electric suction fan.