GF83.40-P-2004RC Regulation of Automatic Air Conditioning, Function
GF83.40-P-2004RC Regulation Of Automatic Air Conditioning, Function
- with CODE (580) Automatic air conditioning
- with CODE (581) Comfort automatic air conditioning
Function requirements, general
^ Circuit 15
^ Automatic air conditioning switched on
^ Circuit 61 (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 interior compartment occurs depending on the settings selected at the AAC [KLA] control and operating unit (N22) (with code (580) Automatic air conditioning) or at 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. interior temperature, outside temperature, coolant temperature).
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 with manual regulation
^ Function sequence for automatic control
(with code (581) Comfort automatic air conditioning)
^ Function sequence of defroster function
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
- Temperature downstream of heater heat exchanger
- Coolant temperature
- Vehicle speed
- Temperature on evaporator
- Refrigerant pressure
- Engine speed
- Door status
- Position of side windows
- Vario roof status
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 addition to the variables listed under manual regulation, the control and operating unit also takes the following variables into consideration:
- Interior temperature
- Solar radiation on the vehicle
- Pollutant concentration of outside air
- Dew point temperature (air humidity of outside air)
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/recirculation flap. These are fully opened.
The flaps for the defroster and side air vents are set so that the maximum air flow is directed toward 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 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.
Function sequence, determining variables
The function sequence for determining variables comprises the following subfunctions:
^ Function sequence, determining the outside temperature
^ Function sequence for determining interior temperature
(with code (581) Comfort automatic air conditioning)
^ Function sequence for determining temperature downstream of the heater heat exchanger
^ 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 for determining door status
^ Function sequence for determining position of side windows
^ Function sequence for determining 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 SAM control unit with fuse and rela 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 measured by the in-car temperature sensor (N22/7b1) (with code (581) Comfort automatic air conditioning) in the control and operating unit.
The in-car temperature sensor is equipped with an aspirator blower which draws in air required for the temperature measurement out of the vehicle interior. The aspirator blower ensures that the vehicle interior air is constantly circulated at the in-car temperature sensor and thus ensures a high degree of control accuracy.
By means of the in-car temperature sensor, a temperature control is achieved which is largely independent of the air flow conditions in the interior compartment.
When the Vario roof is open, the in-car temperature sensor is not evaluated.
Function sequence for determining temperature downstream of the heater heat exchanger
The left heat exchanger temperature sensor (B10/2) and right heat exchanger temperature sensor (B10/3) record the actual temperature of the air flow downstream of the heater heat exchanger.
The recorded values are sent to the control and operating unit.
A comparison takes place here between the measured temperatures (actual value) and preselected specified temperatures (specified value). The duo valve (Y21) opening time is calculated using the comparison of actual and specified value and is then actuated accordingly.
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 ME-SFI [ME] control unit (N3/10) and transmitted via the engine compartment CAN to the central gateway control unit (N93). 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, determining the solar radiation on the vehicle
The control and operating unit uses the sun sensor (B32) to record temperature the angle of incidence and the intensity of the solar radiation on the vehicle. The interior temperature and blower output are adjusted according to the measurements.
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 for determining the temperature on the evaporator
To prevent any icing-up of the evaporator, the temperature there is recorded by the evaporator temperature sensor (B10/6) and read in directly 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 recorded by the refrigerant pressure sensor (B12). The pressure is compared to a stored temperature the pressure curve.
At a refrigerant pressure p < 1.75 bar and p > 30 bar, the refrigerant compressor is switched off.
The refrigerant pressure sensor is read in directly by the driver SAM control unit and transmitted via the interior CAN to the control and operating unit.
Function sequence, determining the engine speed
The engine speed is recorded by the ME-SFI [ME] control unit and transmitted to the central gateway control unit via 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 comfort automatic air conditioning multifunction sensor (B31) records the concentration of the carbon monoxide (CO) and nitrogen oxide (NO X) pollutants.
The values are 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
The comfort automatic air conditioning multifunction sensor uses the ambient temperature and air humidity to calculate the dew point and transmits this data via the AC bus to the control and operating unit. The dew point is needed to regulate the refrigerant compressor.
Function sequence for determining door status
The open and closed state is recorded at the respective door by the left door contact switch (S17/3) and right door contact switch (S17/4).
The door contact switches are read in by the rear SAM control unit with fuse and relay module (N10/2) 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 for determining position of side windows
The respective position is read in by the left door control unit (N69/1) and the right door control unit (N69/2) and sent via the interior CAN to the control and operating unit.
Function sequence for determining Vario roof status
The soft top mechanism control unit (N52) transmits the Vario roof status via the interior CAN 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 for actuation of the 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 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 driver SAM control unit. This receives the request and actuates the compressor control valve.
Function sequence for actuation of the blower motor
Ventilation is achieved with the aid of the blower motor. The control and operating unit transmits a signal from 0 to 100 % via the AC bus to the blower regulator. 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 %.
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 actuates the following components via the AC bus:
- For fresh air/recirculated air control:
- Fresh air/air recirculation flap actuator motor (M2/5)
- for ventilation control:
- Left and right footwell flaps actuator motor (M2/15)
- eft and right defroster flaps actuator motor (M2/16)
- Air flaps actuator motor (M2/21)
(with code (581) Comfort automatic air conditioning)
Function sequence for 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 central gateway 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 then calculates the target fan speed based on the engine temperature and compares this with the request from the air conditioning. The electric fan is actuated accordingly.
