Part 1

GF83.40-P-2004CE Regulation of Automatic Air Conditioning, Function
MODEL 204.0 /2 as of model year 2009 /YoM 08
MODEL 204.3
MODEL 204.9

Function requirements, general
^ Circuit 15 ON
^ Automatic air conditioning switched on
^ Engine running (for cooling operation)
^ Refrigerant compressor (A9) (without code (B09) Refrigerant compressor with magnetic clutch) or refrigerant compressor with magnetic clutch (A9/7) (with code (B09) Refrigerant compressor with magnetic clutch) switched on (for cooling operation)
The electronic ignition lock control unit (N73) sends the status of circuit 15 over the 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) over the chassis CAN (CAN E) and forwarded by the front SAM control unit with fuse and relay module (N10/1) over the interior CAN to the automatic air conditioning control and operating unit (N22/7).

Automatic air conditioning regulation, general
The electronic control of the temperature and the air distribution in the interior is performed depending on the selected settings at the control and operating unit and the variables measured by various sensors (e.g. interior temperature, outside temperature, coolant temperature, vehicle speed).
The determination of these variables will be described following the description of the settings that are relevant for regulation.
The control and operating unit is networked with the vehicle electronics system over the interior CAN, the climate control LIN (LIN B8) and direct lines. 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 evaporator drying process
^ Function sequence for adjustments that are relevant for regulation
^ Function sequence for determining variables
^ Function sequence for AC component actuation

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 the engine switched off the counter in the instrument cluster (A1) is activated. The "Engine OFF" signal is sent by the CDI control unit or the ME-SFI [ME] control unit over the chassis CAN to the instrument cluster.
After a waiting time of t = 1 h the instrument cluster sends the request for the evaporator drying process over 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 sends the request from the blower directly to the blower regulator (A32n1). The blower regulator actuates the blower motor (A32m1) at the lowest blower setting.

Function sequence, adjustments that are relevant for regulation
The function sequence for the control-relevant settings encompasses the following subfunctions:
^ Function sequence for automatic regulation
^ Function sequence for manual regulation
^ Function sequence for defroster function
^ Function sequence, maximum cooling output (with code (494) USA version)

Additional function requirements, automatic regulation
^ "AUTO" button actuated (light-emitting diode (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 on the vehicle
- 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 up to 31.5.10)
- Temperature and moisture on windshield (as of 1.12.09)
- Door status
- Side window position
- Sliding roof position (in model 204.0/2 with code (414) Power glass tilting/sliding roof) or panoramic sunroof position (with code (413) Panoramic glass sunroof with top sliding sunroof)
- Settings on rear automatic air conditioning operating unit (N22/4) (with code (581) Comfort automatic air conditioning)
- Status of the voice control system (VCS [SBS]) (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))

Additional function requirements, manual regulation
^ Air distribution and air volume changed manually (LED in "AUTO" button does not light up)

Function sequence for 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.
The control and operating unit takes the same variables into consideration as with automatic control.
Pressing the "Mono" button (without code (494) USA version) allows the setting of the temperature preselection for the driver side to be adopted for the other zones (passenger side and rear).
For vehicles with code (581) Comfort automatic air conditioning the air distribution currently set on the driver side is also adopted for the passenger side.

Additional function requirements, defroster function
^ "Defrost" button actuated (LED lights up)

Function sequence for defroster function
When the "defrost" button is pressed, all air flaps of the air conditioner housing 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, the air flaps are adjusted during defrosting by the left defroster flap actuator motor (M2/8) for the driver and by the right defroster flap actuator motor (M2/9) for the front passenger. Without code (581)
Comfort automatic air conditioning, common adjustment of the air flap during defrosting for the driver and the front passenger is conducted by the defroster flap actuator motor (M2/16).

Additional function requirements for maximum cooling output (with code (494) USA version)
^ "MAX A/C" button actuated (LED lights up)

Function sequence, maximum cooling output (with code (494) USA version)
Pressing the "MAX A/C" button causes the blower output to be raised to 100 % and the temperature set to "maximum cold".

Function sequence, determining variables
The function sequence for determining the variables encompasses the following subfunctions:
^ Function sequence for determining the outside temperature
^ Function sequence for determining the interior temperature
^ Function sequence for determining the coolant temperature
^ Function sequence for determining the solar radiation on the vehicle
^ Function sequence for determining the vehicle speed
^ Function sequence for determining the temperature at the evaporator
^ Function sequence for determining the refrigerant pressure
^ Function sequence for 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 up to 31.5.10)
^ Function sequence for determining temperature and moisture of windshield (as of 1.12.09)
^ Function sequence for determining the door status
^ Function sequence for determining the side window position
^ Function sequence for determining tilting/sliding roof position (in model 204.0/2 with code (414) Power glass tilting/sliding roof) or the panoramic sunroof position (with code (413) Panoramic glass sunroof with top sliding sunroof)
^ Function sequence for determining settings on rear automatic air conditioning operating unit (with code (581) Comfort automatic air conditioning)
^ Function sequence for determination of VCS status

Function sequence for determining the 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 sends the temperature value over the 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.

Function sequence for determining the interior temperature
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.
On model 204.0/2 with code (414) Power glass tilting/sliding roof, the interior temperature is also recorded in the roof area by the interior temperature sensor with integrated fan (N70b1). The value is read in by the overhead control panel control unit (N70) and sent over the interior CAN to the control and operating unit.
In model 204.0/2 without code (414) Power glass tilting/sliding roof and in model 204.9, the interior temperature is also recorded by the interior temperature sensor with integrated fan (N70/3b1) in the electronic overhead control panel (N70/3). The value is read in directly by the control and operating unit.
These interior temperature sensors are equipped with one ventilation blower each that draws in the air required for measuring the temperature out of the vehicle interior.
The ventilation blower enables constant circulation at the interior temperature sensors, which ensures a high accuracy of temperature measurement and temperature control that is as independent of the airflow ratios in the interior as possible is achieved.
A mean value is calculated from the measurements from the interior temperature sensors. Together with the value of the outside temperature, 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 retained by the control and operating unit when a side window is opened or a door is opened. This ensures that the air conditioning system continues to operate at the set specified temperature.

Function sequence for determining the 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 to control the blend air flaps and the coolant circulation pump (M13/5) (with code (581) Comfort automatic air conditioning or code (B03) ECO start/ stop function).
The value is also used to regulate the PTC heater booster (R22/3) (with diesel engine).

Function sequence for determining the solar radiation on the vehicle
The control and operating unit uses the sun sensor (B32/3) to directly record the angle of incidence of the solar radiation on the vehicle. The interior temperature and blower speed 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.