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

GF83.40-P-2004FQ Regulation of Automatic Air Conditioning, Function
MODEL 218

Function requirements, general
^ Circuit 15 ON
^ Automatic air conditioning switched on
^ Engine running (for cooling operation)
^ Refrigerant compressor (A9) switched on (for cooling mode)
The circuit status of circuit 15 is provided by the electronic ignition lock control unit (N73) via interior CAN (CAN B).
The "Engine running" signal is sent by the CDI control unit (N3/9) (with diesel engine) or by the ME-SFI [ME] control unit (N3/10) (with gasoline engine) via chassis CAN (CAN E) and sent by the front SAM control unit with fuse and relay module (N10/1) via interior CAN.

Automatic air conditioning regulation, general
Electronic control of the temperature and air distribution in the interior is performed depending on the selected settings on the automatic air conditioning control and operating unit (N22/7) and the variables recorded by 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 climate control LIN (LIN B8) 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 control function encompasses the following subfunctions:
^ Function sequence for recording and evaluating variables
^ Regulation function sequence
^ Function sequence for actuating air conditioning components
^ Function sequence for evaporator drying process Function sequence for defroster function
^ Function sequence, maximum cooling output (with code (494) USA version)
If settings are performed at the control and operating unit that affect the temperature, the air distribution or the air volume, the corresponding adjustment values are briefly shown in the Audio/ COMAND display (A40/8).

Function sequence for recording and evaluating variables
The function sequence for determining the variables encompasses the following subfunctions:
^ Outside temperature
^ Interior temperature
^ Coolant temperature
^ Temperature at the air outlets in the vehicle D Solar radiation on the vehicle
^ Vehicle speed
^ Temperature on evaporator
^ Refrigerant pressure
^ Engine speed
^ Door status
^ Side window position
^ Position of tilting/sliding roof (SHD) (with code (414) Power glass tilting/sliding sunroof)
^ Pollutant concentration of the outside air (with code (581) Comfort automatic air conditioning)
^ Settings on rear automatic air conditioning operating unit (N22/4) (with code (581) Comfort automatic air conditioning)
^ VCS [SBS] status (with code (511) Audio 50 APS with DVD changer or with code (512) COMAND APS with DVD changer or with code (527) COMAND APS with single DVD drive (with navigation))
^ Temperature and moisture on windshield

Outside temperature
The outside temperature sensor (B14) measures the outside temperature. The outside temperature sensor signals are read in directly by the front SAM control unit. The front SAM control unit calculates the outside temperature and sends the corresponding value via interior CAN to the control and operating unit.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.

Interior temperature
Head area:
The interior temperature is recorded as follows in the head area:
With code (414) Power glass tilting/sliding sunroof, the interior temperature is recorded in the area of the roof by the interior temperature sensor with integrated fan (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.
Without code (414) Power glass tilting/sliding sunroof, the interior temperature in the area of the roof is recorded by the interior temperature sensor with integrated fan (N70/3b1) in the overhead control panel electronics (N70/3). The signals of the interior temperature sensor with integrated fan are read in by the control and operating unit.
Instrument panel:
The interior temperature is measured by interior temperature sensor (B10/4) in the area of the instrument panel. The signals of the interior temperature sensor are read in directly by the control and operating unit.
The fan sucks in the air for temperature measurement from the vehicle interior.
Because the interior air is constantly circulated by the fan, a very precise temperature measurement is ensured. As a result, a temperature control extremely independent from the air flow conditions in the interior compartment is achieved.
A mean value is calculated from the measurements from the interior temperature sensors. Together with the value of the outside temperature sensor, the mean value is compared to a characteristics map stored in the control and operating unit and used to control the interior temperature.
The mean value of the interior temperature is maintained by the control and operating unit in the following situations:
- Side windows open
- Door open
Immediate further operation of the air conditioning with the specified temperature set can thus be ensured.

Coolant temperature
The coolant temperature is recorded by the coolant temperature sensor (B11/4). The temperature value is read in by the CDI control unit or ME-SFI control unit and transmitted to the front SAM control unit via the chassis CAN. It transmits the value to the control and operating unit via interior CAN.
The value is used for controlling the blend air flaps, for regulating the PTC heater booster (R22/3) (with diesel engine) and for actuating the coolant circulation pump (M13/5) (with code (581) Comfort automatic air conditioning or code (B03) ECO start/stop function).

Temperature at air outlets in vehicle
The temperature on the air outlets is sensed by the left side air vent temperature sensor (B10/31), right side air vent temperature sensor (B10/32), left front footwell vent temperature sensor (B10/35) and right front footwell vent temperature sensor (B10/36). The control and operating unit regulates the outlet air temperature at the respective air outlets.
The signals of the temperature sensors are read in directly by the control and operating unit.

Solar radiation on vehicle
Using the sun sensor (B32/3), the control and operating unit directly records the angle of incidence of the solar radiation on the vehicle.
The interior temperature and the blower speed are adjusted in accordance with the measurements.
In the event of one-sided solar radiation, an adequate temperature difference is set between the left and the right regulated specific temperatures.

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 regulation of the ram air function and for internal calculation of the outside temperature, e.g. in stationary operation.

Temperature at 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.

Refrigerant pressure
The refrigerant pressure is recorded by the refrigerant pressure sensor (B12). The pressure is compared with a stored temperature/ pressure curve. At a refrigerant pressure p < 1.7 bar or p > 30 bar, the refrigerant compressor is switched off.
The signals of the refrigerant pressure sensor are read in directly by the front SAM control unit and forwarded via interior CAN to the control and operating unit.

Engine speed
The engine speed is registered by the CDI control unit or the ME-SFI [ME] control unit and sent over the chassis CAN to the front SAM control unit.
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.

Door status
The left front door rotary tumbler switch (A85s1), right front door rotary tumbler switch (A85/1s1), left rear door rotary tumbler switch (A85/3s1) and right rear door rotary tumbler switch (A85/4s1) record the open and closed statuses at the respective door. The status of the left front door rotary tumbler switch is read in by the left front door control unit (N69/1), the status of the right front door rotary tumbler switch by the right front door control unit (N69/2) and the status of the rear door rotary tumbler switch is read in by the rear SAM control unit with fuse and relay module (N10/2). The values are transmitted to the control and operating unit via the interior CAN.
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.

Side window position
The respective side window position is recorded by the left front door control unit, right front door control unit, left rear door control unit (N69/3) and right rear door control unit (N69/4) and sent via interior CAN to the control and operating unit.

Position of the tilting/sliding roof (with code (414) Power glass tilting/sliding sunroof)
The position of the tilting/sliding roof is read in by the overhead control panel control unit and sent via interior CAN to the control and operating unit.

Pollutant concentration of the outside air (with code (581) Comfort automatic air conditioning)
The pollutant sensor (B31) records the following environmental influences:
- Carbon monoxide (CO)
- Nitrogen oxides (NOx)
- Outside dew point temperature
- Relative humidity
- Ambient temperature
The values are read in directly by the control and operating unit over the climate control LIN. The control and operating unit controls the automatic recirculation according to the read in values.

Settings at the rear automatic climate control operating unit (with code (581) Comfort automatic air conditioning)
The rear compartment climate control functions can be adjusted by the rear passengers using the rear automatic air conditioning control unit. Operating the rockers for temperature and blower setting in the rear automatic air conditioning operating unit is read in and processed over the climate control LIN by the control and operating unit.
This data is used to actuate or regulate the air volume of the rear vents through the rear blower motor (M2/1) and the rear temperature control by the rear blend air flap actuator motor (M2/35). The respective actuation is performed by the control and operating unit via the climate control LIN.

VCS [SBS] status (with code (511) Audio 50 APS incl. DVD changer or with code (512) COMAND APS incl. DVD changer or with code (527) COMAND APS with single DVD drive (with navigation))
With VCS [SBS] active, the blower output is limited.
The radio with auto pilot system (A2/56) (with code (511) Audio 50 APS incl. DVD changer or the COMAND controller unit (A40/3) (with code (512) COMAND APS with DVD changer or with code (527) COMAND APS with single DVD drive (with navigation)) sends the voice control system status over the interior CAN to the control and operating unit.

Temperature and moisture on windshield
The vehicle interior humidity/temperature sensor (B82) measures the relative humidity and temperature directly at the inside of the windshield and uses this to determine the dew point temperature.
The signals of the humidity/temperature sensor are read in by the control and operating unit via climate control LIN.
On vehicles with code (B03) ECO start/stop function, if necessary the engine is started so that the refrigerant compressor runs and the fogging of the windows is thus prevented.

Regulation function sequence
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.
With code (581) Comfort automatic air conditioning:
The temperature, the air distribution and the air volume are automatically regulated.

Function sequence for actuating air conditioning components
The function sequence for actuating the air conditioning components encompasses the following subfunctions:
^ Function sequence for actuation of refrigerant compressor
^ Function sequence, actuation of blower motor (A32m1)
^ Function sequence, actuation of the PTC heater booster (for diesel engine)
^ Function sequence for actuation of the air ducting flaps
^ Function sequence for actuation of combustion engine fan motor and air conditioning with integrated control (M4/7)
^ Function sequence for actuation of coolant circulation pump (M45) (with code (581) Comfort automatic air conditioning or code (B03) ECO start/stop function)

Function sequence for actuation of 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 actuation request over the interior CAN to the front SAM control unit.
This receives the request and actuates the compressor control valve.
The control and operating unit also sends the request for idle speed increase via interior CAN, front SAM control unit and chassis CAN to the ME-SFI [ME] control unit or CDI control unit. This increases the idle speed to match the additional load applied when the refrigerant compressor is switched on.
In vehicles with code (B09) Refrigerant compressor with magnetic clutch a refrigerant compressor with magnetic clutch is installed. To prevent the refrigerant compressor from turning with the air conditioning switched off, the belt pulley is disconnected from the drive shaft of the refrigerant compressor by means of the refrigerant compressor magnetic clutch (A9y1). Fuel is thereby saved.
The control and operating unit sends the request via interior CAN to the front SAM control unit. This directly actuates the refrigerant compressor magnetic clutch.

Function sequence for actuation of blower motor
Ventilation is achieved with the aid of the blower motor. The AAC [KLA] control and operating unit forwards the request straight to the blower regulator (A32n1), which then actuates the blower motor.
With code (581) Comfort automatic air conditioning, the ventilation of the rear passenger compartment is also supported by the rear blower motor. The rear blower motor is actuated via climate control LIN by the control and operating unit.
With VCS [SBS] active, the blower output is limited.
The blower output is limited by the control and operating unit on vehicles with code (B03) ECO start/stop function when the engine stops. To this end, the control and operating unit sends the "Engine stop approved" status from the CDI control unit or the ME-SFI [ME] control unit over the chassis CAN, front SAM control unit and the interior CAN.

Function sequence, actuation of the PTC heater booster (for diesel engine)
When required (e.g. for a cold start) the PTC heater booster is activated via the climate control LIN by the control and operating unit.

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 over the climate control LIN:
Vehicles without code (581) Comfort automatic air conditioning:
- For fresh air/recirculated air control and for ram air control:
- Fresh air/recirculated air 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:
- Defroster flap actuator motor (M2/16)
- Air distribution flap actuator motor (M16/22)
Vehicles with code (581) Comfort automatic air conditioning:
- for fresh air/recirculated air control:
- Fresh air/recirculated air flap actuator motor
- for temperature control:
- Left blend air flap actuator motor
- Right blend air flap actuator motor
- Rear blend air flap actuator motor
- for ventilation control:
- Left defroster flap actuator motor (M2/8)
- Right defroster flap actuator motor (M2/9)
- Left footwell flap actuator motor (M2/10)
- Right footwell flap actuator motor (M2/11)
- Left center air vent flap actuator motor (M2/12)
- Right center air vent flap actuator motor (M2/13)
- Diffuser flap actuator motor (M2/21)
- For ram air control:
- Ram air flap actuator motor (M2/34)

Function sequence for actuation of combustion engine fan motor and air conditioning with integrated control
The fan motor is used for cooling 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 front SAM control unit over the interior CAN.
This sends the request to the CDI control unit or the ME-SFI [ME] control unit over the chassis CAN. The CDI control unit or ME-SFI [ME] control unit then calculates the specified fan speed based on the engine temperature and compares this with the request from the air conditioning. The fan motor is actuated accordingly.

Function sequence for actuation of coolant circulation pump (with code (581) Comfort automatic air conditioning or code (B03) ECO start/stop function)
The coolant circulation pump is used to support the coolant circuit, e.g. at low engine speeds or when using the residual heat utilization function. The control and operating unit sends the request for actuation of the coolant circulation pump over the interior CAN to the front SAM control unit. This then directly actuates the coolant circulation pump.

Additional function requirements for evaporator drying process
^ Air conditioning was active at least once during the ignition sequence
^ Evaporator temperature T > 3 °C
^ Outside temperature T > 20 °C
^ Engine Off
^ Doors closed
^ Kilometer reading > 250 km

Function sequence for evaporator drying process
To counteract any evaporator odor in the interior and any fogging of windows when starting the air conditioning, an evaporator drying process is conducted at the air conditioning system.
With circuit 61 OFF, the timer is activated in the instrument cluster.
The circuit status is read in by the CDI control unit or by the ME-SFI [ME] control unit over the chassis CAN and sent to the instrument cluster.
After a waiting time of t = 1 h the instrument cluster sends the request for the evaporator drying process via the interior CAN to the control and operating unit which then starts the evaporator drying process. To this end, the blower is activated at the lowest setting for t = 30 min.
The control and operating unit transmits the request from the blower directly to the blower regulator. The blower regulator actuates the blower motor at the lowest blower stage.

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/recirculated air flap.
These are fully opened. The defroster 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 is actuated by the control and operating unit via the blower regulator 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.
With code (581) Comfort automatic air conditioning, defrost mode occurs separately by means of the left defroster flap actuator motor for the driver and the right defroster flap actuator motor for the front passenger.
Without code (581) Comfort automatic air conditioning, the regulation for the driver and the front passenger occurs together by means of the defroster flap actuator motor.

Additional function requirements, maximum cooling output (with code (494) USA version)
^ "MAX COOL" button actuated (LED illuminated)

Function sequence, maximum cooling output (with code (494) USA version)
Pressing the "MAX COOL" button causes the blower output to be raised to 100 % and the temperature set to "maximum cold". "MAX COOL" is shown on the display.