Climate control regulation, function

P83.40-4909-79

Function requirements, general

For regulating the climate control:

 Terminal 15 ON

 Automatic air conditioning switched on

For cooling operation:

 Engine running

 Refrigerant compressor on (not switched off via the climate control control unit)

For evaporator drying process:

 Engine Off

 The electronic ignition lock control unit sends the status of terminal 15 via interior CAN to the A/C control unit.
The ME-SFI [ME] control unit sends the "Engine running" signal via the drive train CAN, powertrain control unit, chassis CAN 1, front SAM control unit, and interior CAN to the climate control control unit.

Climate control, general

The electronic temperature control and the air distribution in the vehicle interior are regulated to match the configured settings, and the variables (e.g. vehicle interior temperature, outside temperature, coolant temperature and vehicle speed) recorded by various sensors. Settings can be made on the climate control operating unit and through the air conditioning menu in the head unit.

The climate control control unit is networked with the vehicle electronics via the interior CAN, climate control LIN 1, and climate control LIN. 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:

 Recording and evaluation of variables

 Actuation of air conditioning components

 Fresh air mode

 Recirculated air mode

 Defrost function

 Evaporator drying

Recording and evaluation of variables

The following variables are recorded and evaluated:

 Outside temperature

 Interior temperature

 Temperature at the air outlets in the vehicle

 Temperature and moisture on windshield

 Dewpoint temperature

 Coolant temperature

 Temperature on evaporator

 Refrigerant pressure

 Solar radiation

 Air quality

 Vehicle speed

 Engine speed

 Soft top status (model 190.4)

 Door status

 Side window position

 Operating settings

 Voice control system (VCS) status (with code 506 (Audio 20 NTG 5.5 radio) or code 531 (COMAND APS))

Outside temperature

The outside temperature sensor measures the outside temperature. The front SAM control unit reads in the signal of the outside temperature sensor directly, calculates the outside temperature and transmits it to the A/C control unit over the interior CAN. The A/C control unit requires this value to achieve the required 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 only taken into account if the vehicle speed for a minimum period of 30 s is greater than 30 km/h. The last measured value is used for speeds below 30 km/h and when the ignition is switched on and off.

Interior temperature

Roof area:

The vehicle interior temperature in the roof area is recorded by the interior temperature sensor with integrated fan in the overhead control panel electronics. The climate control control unit directly reads in the signal from the interior temperature sensor. The integrated fan sucks in air for temperature measurement from the vehicle interior.

 Because the interior air is constantly circulated by the fan, a precise temperature measurement is ensured. This enables a temperature control to be achieved that is mainly independent of the airflow conditions in the vehicle interior.

Instrument panel:

The interior temperature in the instrument panel area is recorded by the interior temperature sensor. The climate control control unit directly reads in the signal from the interior temperature sensor.

A mean value is calculated from the measurements of both interior temperature sensors. Together with the outside temperature, this mean value is compared to a characteristics map stored in the climate control control unit and used to control the interior temperature.

The mean value of the interior temperature is maintained by the climate control control unit in the following situations:

 Side window open

 Door open

 Open soft top (model 190.4)

This ensures that the air conditioning system immediately continues operation at the set specified temperature.

Temperature at the air outlets in the vehicle

The temperatures at the air outlets in the vehicle are recorded by the air outlet temperature sensors. The climate control control unit reads in the signals from the outlet air temperature sensors directly. The A/C control unit regulates the air outlet temperatures at each of the air outlets.

Temperature and moisture on windshield

The temperature and relative air humidity (dewpoint temperature) on the inside of the windshield are measured by the vehicle interior humidity and temperature sensor. Fogging up of the windshield can therefore be recognized. The climate control control unit reads in the signals from the vehicle interior humidity and temperature sensors over the air-conditioning control LIN 1. If the windshield threatens to fog up, corresponding countermeasures are taken such as, e.g. switching in the refrigerant compressor.

Dewpoint temperature

The dew point is determined from the ambient temperature and the air humidity. The climate control control unit reads in the signals from the dew point sensor via the climate control LIN 1 and calculates the dew point. When the dew point is reached, the automatic flap mechanism prevents the outside of the windshield from fogging up.

Coolant temperature

The coolant temperature is recorded by the coolant temperature sensor. The ME-SFI [ME] control unit reads in the signals from the coolant temperature sensor directly, uses them to calculate the coolant temperature and sends this over the drive CAN, powertrain control unit, chassis CAN 1, front SAM control unit and the interior CAN to the climate control control unit.

The value is used to control the blend air flaps and to actuate the coolant circulation pump.

Temperature on evaporator

To prevent the evaporator from icing up, the temperature there is recorded by the evaporator temperature sensor. The signals of the evaporator temperature sensor are read in directly by the A/C control unit. If the evaporator temperature drops below 2 °C, the refrigerant compressor is switched off. As from a temperature of 2.5 °C, the refrigerant compressor is switched on again.

Refrigerant pressure

The refrigerant pressure is recorded by the refrigerant pressure sensor. The climate control control unit reads in the signals from the refrigerant pressure sensor directly. The pressure is compared with a stored temperature/pressure curve. At a refrigerant pressure of less than 0.8 or above 30 bar the refrigerant compressor is switched off or not activated. From a refrigerant pressure of more than 0.9 bar the refrigerant compressor is switched on or activated again.

Solar radiation

The angle of incidence and the intensity of the solar radiation in the vehicle are recorded by the sun sensor. The climate control control unit directly reads in the signals from the sun sensor. The blowing air temperature and the blower speed are adjusted in accordance with the values. In the event of one-sided solar radiation, an appropriate temperature difference is set between the left and the right specified control temperatures.

Air quality

The air quality sensor records the concentration level for the following pollutant gases in the outside air:

 Carbon monoxide (CO)

 Nitrogen oxides (NOx)

The climate control control unit reads in the signals from the air quality sensor via the climate control LIN 1. The A/C control unit realizes the automatic air recirculation according to the read-in values.

Vehicle speed

The vehicle speed is calculated by the instrument cluster. The instrument cluster sends the vehicle speed via user interface CAN, gateway AMG control unit and interior CAN to the climate control control unit.

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.

Engine speed

The engine speed is recorded by the ME-SFI [ME] control unit. The ME-SFI [ME] control unit sends the engine speed over the drive CAN, powertrain control unit, chassis CAN 1, front SAM control unit and the interior CAN to the climate control control unit.

The engine speed is used to regulate the refrigerant compressor, among other things.

Soft top status (model 190.4)

The position of the soft top is detected by the control unit for the soft top control. The control unit for the soft top control sends the status of the soft top over the interior CAN to the climate control control unit.

When the soft top is opened, the climate control control unit references the values of the interior temperature sensors and adapts the temperature control accordingly. If there is a large difference in temperature between the interior air and outside air, unnecessary readjustment is avoided.

Door status

The status of each door is determined by the following control units and transmitted via the interior CAN to the A/C control unit:

 Left door control unit

 Right door control unit

When a door is opened, the climate control control unit references the values of the interior temperature sensors and adapts the temperature control accordingly. If there is a large difference in temperature between the interior air and outside air, unnecessary readjustment is avoided.

Side window position

The respective side window position is determined by the left door control unit or right door control unit and sent via the interior CAN to the climate control control unit.

When a side window is lowered, the climate control control unit references the values of the interior temperature sensors and adapts the temperature control accordingly. If there is a large difference in temperature between the interior air and outside air, unnecessary readjustment is avoided.

Operating settings

The settings for climate control of the vehicle interior can be made at the following control points:

 Climate control operating unit

 Head unit

 VCS (as of 01.12.2018)

Climate control operating unit

The climate control operating unit has the following buttons which are used for making the various settings:

 Left temperature selection button

 Air recirculation mode button

 Rear window heater button

 Right temperature selection button

 Climate control menu button

 Air distribution button, left

 "SYNC" button

 "A/C" button

 Blower button

 AUTO button

 Defrosting button

The climate control operating unit sends information regarding the settings via the climate control LIN to the climate control control unit. This information is used to regulate the air flow, air distribution and temperature. The selected settings are additionally displayed on the Audio/COMAND display. For this purpose, the climate control control unit sends the relevant information via the interior CAN, the AMG gateway control unit and the user interface CAN to the head unit. The head unit generates the corresponding image data and sends a switch-on request to the Audio/COMAND display via telematics CAN. The image data is sent via the LVDS line to the Audio/COMAND display.

 For feedback on the function, the A/C control unit transmits the request for LED actuation via the climate control LIN to the climate control operating unit.

Head unit

The air conditioning menu in the head unit can be used to switch off the air conditioning system or to select the climate control functions. The head unit sends corresponding information over the user interface CAN, AMG gateway control unit and the interior CAN to the climate control control unit.

The head unit also generates the corresponding picture data, sends a switch-on request over the telematics CAN to the Audio/COMAND display and sends the picture data over the LVDS line to the Audio/COMAND display.

VCS (as of 01.12.2018)

Individual air conditioning system functions can also be operated through the VCS. The head unit evaluates the contents of the voice commands and sends corresponding requests over the user interface CAN, AMG gateway control unit and the interior CAN to the climate control control unit.

VCS status (with code 506 (Audio 20 NTG 5.5 radio) or code 531 (COMAND APS))

When the VCS is active, the climate control control unit reduces the output of the blower motor using the blower regulator. The head unit sends the status of the VCS via the user interface CAN, AMG gateway control unit, and interior CAN to the climate control control unit.

Actuation of air conditioning components

Actuation of the air conditioning components encompasses the following subfunctions:

 Actuation of blower motor

 Actuation of air ducting flaps

 Actuation of refrigerant compressor

 Actuation of fan motor

 Actuation of coolant circulation pump

Actuation of blower motor

Ventilation of the vehicle interior is achieved with the aid of the blower motor. The climate control control unit directly actuates the blower motor via the blower regulator.

 Model 190
with code 506 (Audio 20 NTG 5.5 radio)
Model 190
with code 531 (COMAND APS)
With VCS [SBS] active, the blower setting is reduced.

Actuation of 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 are adjusted:

 Fresh air/recirculated air flap via the fresh air/recirculated air flap actuator motor (fresh air/recirculated air control)

 Left blend air flap via left blend air flap actuator motor (temperature control)

 Right blend air flap via the right blend air flap actuator motor (temperature control)

 Footwell flap via footwell flap actuator motor (ventilation control)

 Defroster flap over the defroster flap actuator motor (ventilation control)

 Center air vent flap over the center air vent flap actuator motor (ventilation control)

 Ram air flap over the ram air flap actuator motor (ram air control)

The A/C control unit actuates the actuator motors over the climate control LIN 1.

 To prevent any fogging of the windows, 2 minutes after switching off circuit 15, the defroster flap and the footwell flap are opened. After starting the engine, the defroster flap remains for approx. 30 s in their fixed position, after which all the setting options are available again.

 With circuit 15 Off, the fresh/recirculated air flap is moved to 50 % by the fresh/recirculated air flap actuator motor when one of the doors is opened. The door closing forces are thereby reduced. The function can be set with the diagnostic tester.

P83.10-2873-79

Actuation of refrigerant compressor

The refrigerant compressor is responsible for induction and compression of the refrigerant. The output of the refrigerant compressor is continuously regulated by the climate control control unit using the refrigerant compressor regulation valve. The climate control control unit sends the request to actuate the refrigerant compressor via the interior CAN to the front SAM control unit. The front SAM control unit directly actuates the refrigerant compressor regulating valve.

The climate control control unit also sends the calculated torque from the refrigerant compressor via the interior CAN, front SAM control unit, chassis CAN 1, powertrain control unit, and drive train CAN to the ME-SFI [ME] control unit. This keeps the idle speed constant in accordance with the additional load that occurs when the refrigerant compressor is switched on.

Actuation of fan motor

The fan motor is used for cooling the coolant and refrigerant. The climate control control unit calculates the specified fan speed in relation to the refrigerant pressure and sends this over the interior CAN, front SAM control unit, chassis CAN 1, powertrain control unit and the drive CAN to the ME-SFI [ME] control unit.

The ME-SFI [ME] control unit corrects the requested target fan speed depending on the engine temperature and actuates the fan motor accordingly.

Actuation of coolant circulation pump

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.

At low engine rpm, the coolant circulation pump is also actuated to ensure that the flow volume needed to heat up the air flowing past is adequate. The climate control control unit actuates the coolant circulation pump directly. When the engine is switched off, the coolant circulation pump is also actuated.

Fresh air mode

The fresh air/ram air flap is open during fresh air mode. Fresh air is fed through the air conditioning housing and into the vehicle interior.

The climate control control unit actuates the fresh/recirculated air flap actuator motor over the air-conditioning control LIN 1.

Recirculated air mode

Air recirculation mode encompasses the following subfunctions:

 Air recirculation mode via the air recirculation mode button

 Pollutant-controlled air recirculation mode

Air recirculation mode via the air recirculation mode button

Pressing the air recirculation mode button on the climate control operating unit closes the fresh air/recirculated air flap to prevent the air supply from outside. The air only circulates in the vehicle interior. This keeps unpleasant odors and pollutants away. The LED in the air recirculation mode button lights up during air recirculation mode.

The climate control control unit reads in the status of the air recirculation mode button via the climate control LIN and actuates the fresh air/recirculated air flap actuator motor via the climate control LIN 1.

Vehicles without CODE 494 (USA version):

When the air recirculation mode button is pressed, the side windows are closed. If the air recirculation mode button is then pressed, the side windows are moved back to the default position (insofar as they were not manually adjusted during air recirculation mode).

Additional function requirements for pollutant- controlled air recirculation mode

 Refrigerant compressor switched on

Pollutant-controlled air recirculation mode

The air quality sensor records the concentration level for the following pollutant gases in the outside air.

The air quality sensor sends corresponding information over the air-conditioning control LIN 1 to the climate control control unit. From a specific pollutant concentration onwards, the climate control control unit closes the fresh/recirculated air flap. Outside air supply is prevented and only the inside air is recirculated. If, after starting the engine, the condition for pollutant-sensitive air recirculation mode is given, then fresh air is initially supplied for 30 s. After this, operation continues with 80 % of the pollutant-sensitive air recirculation mode and after another 10 s, as required, 100 % of the pollutant-sensitive air recirculation mode.

 The pollutant-controlled air-recirculation mode is not indicated by the LED of the air-recirculation mode button.

 The pollutant-controlled air-recirculation mode is active for a maximum of 30 minutes.

Defrost 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 flap is adjusted so that the maximum air flow is directed to the windshield and the front side windows. The blend air flaps are moved in relation to the outside temperature. The maximum opening is thereby limited so that the blowing air temperature does not exceed 80 °C.

The climate control 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 also switched on to dry the outflowing air.

Additional function requirements for evaporator drying process

 Air conditioning was active at least once during the last ignition cycle

 Outside temperature above 20 °C

 Doors closed

 Kilometer reading over 250 km

Evaporator drying

To counteract evaporator odors in the vehicle interior and fogging of windows when starting the air conditioning, an evaporator drying process is performed.

After the engine is switched off, the climate control control unit sends the signal to activate the evaporator drying process timer via the interior CAN, AMG gateway control unit, and user interface CAN to the instrument cluster. The ME-SFI [ME] control unit sends the "Engine running" signal via the drive train CAN, powertrain control unit, chassis CAN 1, AMG gateway control unit, and interior CAN to the climate control control unit.

After a waiting time of 1 h the instrument cluster sends a request for evaporator drying over the user interface CAN, AMG gateway control unit and the interior CAN to the climate control control unit that starts the evaporator drying process. The blower motor is actuated for this at the lowest stage for 30 minutes..

The climate control control unit transmits the request directly to the blower regulator. The blower regulator actuates the blower motor at the slowest speed. The air supply serves to reduce residual moisture in the evaporator.