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Climate Control Regulation, Function - GF83.40-P-2012KJ

MODEL 453.0 (except 453.091), 453.3 (except 453.391), 453.4 (except 453.491) 

G12096999Courtesy of MERCEDES-BENZ USA

Shown on model 453.0/3 with code I01 (Automatic air conditioning system) 

G12097000Courtesy of MERCEDES-BENZ USA

Shown on Model 453.0/3 without code I01 (Automatic air conditioning system) or with code I77 (Manual A/C system) 

Function requirements, general 

For cooling mode (only vehicles with code I01 (Automatic air conditioning) or with code I77 (Manual A/C system)):

IMPORTANT The center SAM control unit activates the air conditioning system power supply solenoid switch with circuit 15 ON. The circuit 15 status of the ignition lock is received by the center SAM control unit over a direct line from the vehicle interior fuse and relay module.

The ME-SFI [ME] control unit transmits the "Engine running" signal via the interior CAN to the climate control unit.

Climate control, general 

On vehicles with code I01 (Automatic air conditioning), the electronic temperature control and the air distribution in the vehicle interior is dependent on the settings made on the climate control operating unit, and the variables recorded using various sensors (e.g. interior temperature, outside temperature, coolant temperature, vehicle speed). Determination of these variables is described below.

On vehicles without code I01 (Automatic air conditioning), the temperature control and air distribution in the vehicle interior is mechanically conducted by the climate control and operating unit using Bowden cables to the individual air distribution and blend flaps. Only the rear window heater and the blower motor are electrically actuated or regulated. On vehicles with code I77 (Manual A/C system), the air conditioning is also switched on using the A/C button, whereupon the solenoid clutchof the A/C compressor is switched on and electrically activated

IMPORTANT Detailed information about possible settings is available in the separate component description for the "Climate control operating unit". On vehicles with code I01 (Automatic air conditioning) the Climate control unit is networked over the interior CAN, telematics CAN and the climate control LIN to the vehicle electronics. This in turn makes it possible to incorporate relevant parameters in order to improve regulation quality and to lower power consumption.

The climate control regulation function encompasses the following subfunctions:

Function sequence for recording and evaluating variables 

The following variables are recorded and assessed, and depending on the A/C system installed, these then exert an influence on the regulation of the climate control:

Outside temperature variable (only vehicles with code l01 (Automatic air conditioning) or with code l77 (Manual A/C system))  The outside temperature sensor measures the outside temperature. The instrument cluster reads in the outside temperature sensor signal directly, calculates the outside temperature and sends this over the interior CAN to the ME-SFI [ME] control unit, which then uses the outside temperature value to regulate the refrigerant compressor.

On vehicles with code I01 (Automatic air conditioning), the climate control unit receives the outside temperature via interior CAN.

The A/C control unit requires this value to achieve the required interior temperature by adjusting the blend air flaps accordingly.

IMPORTANT If the vehicle is stationary, the measured temperature can differ considerably from the outside temperature. This is why the outside temperature is only taken account for the regulation, if the vehicle speed was more than v = 30 km/h for a period of at least t = 30 s. At speeds of v < 30 km/h as well as when switching the ignition on and off, the temperature value measured last is used.

Temperature in vehicle interior and moisture on windshield variable (only vehicles with code l01 (Automatic air conditioning)) 

The vehicle interior humidity and temperature sensor measures the relative humidity and temperature in the vehicle interior directly at the inside of the windshield and uses this to determine the dew point temperature. The surface temperature on the windshield and the interior temperature are also determined. The comparison with the dew point temperature enables any (impending) fogging of the windshield to be detected. The signals of the vehicle interior humidity and temperature sensor are read in directly by the climate control unit.

If the windshield threatens to fog up, corresponding countermeasures are taken such as switching in the refrigerant compressor.

Coolant temperature variable 

The coolant temperature is recorded by the coolant temperature sensor. The ME-SFI [ME] control unit reads in the resistance value of the coolant temperature sensor directly, uses it to calculate the coolant temperature and transmits this via the interior CAN to the climate control unit. The value is used for controlling the PTC heater and on vehicles with code I01 (Automatic air conditioning), for controlling the blend air flaps. Temperature on evaporator variable (only vehicles with code l01 (Automatic air conditioning) or with code l77 (Manual A/C system))  To prevent the evaporator from icing up, the temperature there is recorded by the evaporator temperature sensor. The signals from the evaporator temperature sensor are read in and evaluated directly, with code I01 (Automatic air conditioning), by the climate control unit.

If the evaporator temperature drops to approx. T = 2°C, the refrigerant compressor is switched off. To do so, the climate control unit sends the corresponding signals for switching on and off over the interior CAN to the ME-SFI [ME] control unit. With code I77 (Manual A/C system), the signal from the evaporator temperature sensor is read in over a direct line from the climate control and operating unit, this evaluates the signal and adapts the direct signal for switching on and off the refrigerant compressor to the ME-SFI [ME] control unit.

Refrigerant pressure variable (only vehicles with code l01 (Automatic air conditioning) or with code l77 (Manual A/C system))  The refrigerant pressure is recorded by the coolant pressure sensor. The signals from the coolant pressure sensor are read in directly by the ME- SFI [ME] control unit. The pressure is compared with a stored temperature/pressure curve. The refrigerant compressor is switched off or not switched in at a refrigerant pressure of p < 0.8 bar and p > 30 bar. The refrigerant compressor is switched in again from a refrigerant pressure of p > 0.9 bar.

Solar radiation variable (only vehicles with code l01 (Automatic air conditioning)) 

The angle of incidence and the intensity of the solar radiation in the vehicle are recorded by the sun sensor in the rain/light sensor. The rain/light sensor reads in the signals from the sun sensor directly, evaluates them and forwards information about the solar radiation over the rain/light sensor LIN, driver-side SAM control unit and the interior CAN to the climate control unit. The blowing air temperature and the blower speed are adjusted in accordance with the values.

Vehicle speed variable (only vehicles with code l01 (Automatic air conditioning) or with code l77 (Manual A/C system)) 

The vehicle speed is sent by the Electronic Stability Program control unit over the interior CAN to the ME-SFI [ME] control unit, and on vehicles with code I01 (Automatic air conditioning) to the climate control unit. It is used for internal computation of the outside temperature, e.g. when in stationary mode and also for regulation of the fan, depending on the vehicle speed.

On vehicles with code I01 (Automatic air conditioning), the vehicle speed is used for regulating the ram air function.

Engine speed variable (only vehicles with code l01 (Automatic air conditioning) or with code l77 (Manual A/C system)) 

The engine rpm is recorded by the ME-SFI [ME] control unit through the crankshaft position sensor, and sent over the interior CAN to the climate control unit. The engine speed is used among others to regulate the refrigerant compressor.

Settings on the climate control operating unit (only vehicles with code l01 (Automatic air conditioning)) 

The climate control of the driver and front passenger compartment can be adjusted using the following buttons at the climate control operating unit:

The settings are transmitted by the climate control operating unit via the climate control LIN to the climate control unit where they are processed. The data are used to regulate the air volume, air distribution and temperature. The selected settings are displayed on the Smart Radio Multimedia Navigator Display.

The selected settings are transmitted to the Smart Radio Multimedia Navigator by the climate control operating unit via the interior CAN, the audio gateway control unit and the telematics CAN.

IMPORTANT For feedback on the function, the climate control unit transmits the request for LED actuation via the climate control LIN to the climate control operating unit.

Settings on the climate control and operating unit (vehicles without code l01 (Automatic air conditioning)) 

The climate control of the driver and front passenger compartment can be adjusted using the following buttons at the climate control operating unit:

The settings on the climate control and operating unit are read in and processed by it directly. The data are then used to regulate the air flow, rear window heater and the A/C system. The air distribution and temperature control are performed mechanically through air distribution and blend air flaps. Control feedback is realized via the LEDs integrated into the selector wheels and buttons, that are directly actuated by the climate control and operating unit.

AC component actuation function sequence 

The function sequence for actuating the A/C components encompasses the following subfunctions:

Function sequence for actuation of blower motor 

Ventilation is achieved with the aid of the blower motor.

On vehicles with code I01 (Automatic air conditioning), the blower motor is regulated through the blower regulator. For this purpose, the climate control unit actuates the blower regulator directly, which regulates the blower motor.

On vehicles without code I01 (Automatic air conditioning), the blower motor is actuated directly by the climate control and operating unit. The blower settings are regulated through the respective blower motor series resistor.

Function sequence for actuation of the air ducting flaps 

The air distribution in the vehicle interior is controlled by adjusting the air ducting flaps in the air conditioner housing.

The following air-ducting flaps on vehicles with code I01 (Automatic air conditioning) are electrically adjusted by actuator motors:

The climate control unit actuates the actuator motors directly.

On vehicles without code I01 (Automatic air conditioning), adjustment of the above-mentioned flaps is performed mechanically through Bowden cables, that are each connected to the air distribution selector wheel, air volume selector wheel and temperature selector wheel.

Air outlets in cockpit 

G12097001Courtesy of MERCEDES-BENZ USA

Function sequence for actuation of refrigerant compressor (only vehicles with code l01 (Automatic air conditioning) or with code l77 (Manual A/C system)) 

The refrigerant compressor is responsible for induction and compression of the refrigerant.

On vehicles with code I01 (Automatic air conditioning), the refrigerant compressor power is regulated by the climate control unit. The climate control unit transmits the request to actuate the refrigerant compressor via the interior CAN to the ME-SFI [ME] control unit.

On vehicles with code I77 (Manual A/C system), the ME-SFI [ME] control unit receives the request to switch on the refrigerant compressor over a direct line from the climate control and operating unit. The refrigerant compressor is switched on using the "A/C" button in the climate control and operating unit.

The ME-SFI [ME] control unit switches the magnetic clutch of the refrigerant compressor on or off depending on the status over the refrigerant compressor relay. The ME-SFI [ME] control unit also keeps the idle speed constant, according to the additional load that occurs when the refrigerant compressor is switched on.

Function sequence for actuation of the fan motor 

The fan motor is used for cooling the coolant and refrigerant.

On vehicles with code I01 (Automatic air conditioning), the climate control unit calculates the specified fan speed depending on the refrigerant pressure, and sends a request over the interior CAN to the ME-SFI [ME] control unit. The ME-SFI [ME] control unit then calculates the specified fan speed depending on the engine temperature and the charge air temperature along with the request from the climate control unit and the refrigerant temperature, before then actuating the fan motor accordingly.

On vehicles with code I77 (Manual A/C system), the ME-SFI [ME] control unit controls the fan speed depending on the coolant pressure sensor, coolant temperature sensor and the charge air temperature sensor.

Function sequence, heating mode 

Additional function requirements:

Driven by the coolant pump, the coolant circulates in the engine cooling circuit. In the process, it absorbs engine heat. The heated coolant passes through the heater heat exchanger, which dissipates heat to the air blowing by.

On vehicles with code I01 (Automatic air conditioning), the climate control unit regulates the interior temperature set by the temperature control of the climate control operating unit. To do so, it actuates the blend air flap actuator motor directly and regulates the inflow temperature (blow air temperature) of the heating air with the aid of the vehicle interior humidity and temperature sensor.

On vehicles without code I01 (Automatic air conditioning), the temperature is adjusted using the temperature selector wheel, which uses a Bowden cable to mechanically actuate the blend air flap.

Heater booster through PTC heater on vehicles with code V69 (Heating element for cold countries) 

For cold outside temperatures and a low coolant temperature in the engine's coolant circuit, the air flowing into the interior is also heated up by an electric PTC heater, which is located in the air conditioner housing behind the heat exchanger. The PTC heater has a total power consumption of 900 W at 0 °C and it can be actuated by the center SAM control unit to meet requirements in 3 stages. Therefore, at an air temperature of, e.g. 0 °C, the first stage with an output of 300 W is actuated together with the second stage with a 600 W output, so that the air flowing into the passenger compartment is heated at an output of 900 W. As air temperature increases, only the second stage with 600 W and then only the first stage with 300 W is actuated. Similarly, as temperature increases, the electrical resistance of the PTC heater increases and the power consumption of the individual heating stages drops proportionally. On vehicles with code I01 (Automatic air conditioning), the climate control unit sends the request to switch on the individual heating stages over the interior CAN to the center SAM control unit. This then actuates the PTC heater booster through the electric heater booster solenoid switch, Stage 1 (K16/2) or through the electric heater booster solenoid switch, Stage 2 (K16/3). On vehicles without code I01 (Automatic air conditioning), the control logic is implemented in the center SAM control unit.

Fresh air mode function sequence 

The fresh air/recirculated air flap is open and fresh air is delivered into the vehicle interior through the air conditioner housing.

Air recirculation mode function sequence 

By operating the air recirculation mode button at the climate control operating unit (with code I01 (Automatic air conditioning)) or the fresh air/air recirculation mode switch (without code I01 (Automatic air conditioning)), the fresh air/recirculated air flap is closed, to prevent any air entering from the outside. The air only circulates in the vehicle interior. This keeps unpleasant odors and pollutants away. The LED in the air recirculation mode button or on the fresh air/air recirculation mode switch lights up during the air recirculation mode.

On vehicles with code I01 (Automatic air conditioning), the climate control unit reads in the status of the air recirculation mode button over the climate control LIN, and actuates the fresh air/recirculated air flap actuator motor directly.

On vehicles without code I01 (Automatic air conditioning), the fresh air/recirculated air flap is mechanically operated by a Bowden cable using the fresh air/air recirculation mode switch.

Function sequence for defrost function (only vehicles with code l01 (Automatic air conditioning)) 

When the defroster button is pressed, all air flaps are closed with the exception of the fresh air/recirculated air flap. This is fully opened. The blend air flap is moved depending on the outside temperature - the maximum opening is limited so that the specified blowing air temperature of approx. T = 80 °C is not exceeded.

The climate control unit actuates the blower regulator, and this actuates the blower motor so that optimum defrost mode is provided depending on the exhaust air temperature.

The refrigerant compressor is activated in order to ensure that the air flowing out is dried. The PTC heater is also switched-in. The air is dried and then heated up.

  Electrical function schematic for climate control input signals Vehicles with code I01 (Automatic air conditioning) PE83.40-P-2056-97BBA 
Vehicles with code I77 (Manual A/C system) PE83.40-P-2056-97BBB 
  Electrical function schematic for climate control actuation   PE83.40-P-2057-97BBA 
  Overview of system components for climate control   GF83.40-P-9994KJ 
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