Climate control regulation, function

S83.40-4565-79

Function requirements, general

 Circuit 15 ON

For cooling operation:

 Engine runs

 A/C compressor with magnetic clutch (A9/10) switched on

 The circuit 15 status is sent by the electronic ignition lock (EZS) control unit (N73) over the interior CAN (CAN B) to the automatic air conditioning (AAC) control unit (N154). The "Engine running" signal is sent by the CDI control unit (N3/33) or the ME-SFI [ME] control unit (N3/34) (with engine 274) via chassis CAN (CAN E) to the electronic ignition lock (EZS) control unit (N73) and is forwarded from there via interior CAN (CAN B) to the instrument cluster (IC [KI]) control unit (A1/1) and the automatic air conditioning (AAC) control unit (N154).

Climate control, general

The climate control operates dependent on the signals recorded by the automatic air conditioning (AAC) control unit (N154) (e.g. interior temperature, outside temperature, coolant temperature, vehicle speed) and the settings selected on the FRONT heater/air conditioning operating unit switch (S98/1) or on the radio (Audio/COMAND) (N87/6). In vehicles with code HZ7 (Semi-automatically controlled A/C, TEMPMATIC in rear) the settings selected on the REAR heater/air conditioning operating unit switch (S98/2) are also included.

The climate control regulation function encompasses the following subfunctions:

 Function sequence for recording and evaluating signals

 AC component actuation function sequence

 Function sequence for defroster function

 Function sequence for evaporator drying process

 Function sequence for residual heat utilization (with CODE HH4 (THERMOTRONIC automatic climate control))

 Function sequence for shutoff of air conditioning after an accident (crash signal sent)

Function sequence for recording and evaluating signals

The following signals are recorded and evaluated:

 Outside temperature

 Interior temperature

 Temperature at left and right footwell air vents (with CODE HH4 (THERMOTRONIC automatic climate control))

 Temperature and moisture on windshield

 Coolant temperature

 Evaporator temperature

 Refrigerant pressure

 Solar radiation

 Vehicle speed

 Door status

 Settings on FRONT heater/air conditioning operating unit switch (S98/1)

 Settings on REAR heater/air conditioning operating unit switch (S98/2) (with code HZ7 (Semi-automatically controlled A/C, TEMPMATIC in rear))

 Settings on radio (Audio/COMAND) (N87/6)

Outside temperature

The signal acquisition and actuation module (SAM) control unit (N10/1) reads in the outside temperature sensor (B14) signal directly, calculates the outside temperature and sends this over the interior CAN (CAN B) to the automatic air conditioning (AAC) control unit (N154). The automatic air conditioning (AAC) control unit (N154) requires this value to enable the desired interior temperature to be reached 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 greater than 30 km/h for a period of at least 30 seconds. The previously measured temperature is used at speeds of less than 30 km/h and when the ignition is being switched on and off.

Interior temperature

The interior temperature is recorded by the interior air temperature sensor (M9b1) of the blower with interior air temperature sensor (M9). The automatic air conditioning (AAC) control unit (N154) sends a request over the blower regulator to the blower with interior temperature sensor (M9). The blower (M9m1) is then actuated. The blower (M9m1) sucks in the air for the temperature measurement from the vehicle interior. The automatic air conditioning (AAC) control unit (N154) reads in the interior temperature value directly.

Temperature at left and right footwell air vents (with CODE HH4 (THERMOTRONIC automatic climate control))

The temperatures at the footwell air outlets are recorded by the left footwell air outlet temperature sensor (B73) or right footwell air outlet temperature sensor (B74). The signals are read in directly by the automatic air conditioning (AAC) control unit (N154). The automatic air conditioning (AAC) control unit (N154) regulates the air outlet temperature at the respective air outlets.

Temperature and moisture on windshield

The temperature and the relative air humidity (dew point temperature) on the inside of the windshield is recorded by the humidity sensor of the humidity sensor/light sensor/rain sensor/sun sensor (B38/3).

The humidity sensor/light sensor/rain sensor/sun sensor (B38/3) sends the corresponding signal over the roof LIN (LIN B13) to the signal acquisition and actuation module (SAM) control unit (N10/1). The signal acquisition and actuation module (SAM) control unit (N10/1) calculates the dew point temperature and sends the signal over the interior CAN (CAN B) to the automatic air conditioning (AAC) control unit (N154). The automatic air conditioning (AAC) control unit (N154) uses the dew point temperature to calculate the relative air humidity and the temperature of the inside of the windshield.

Coolant temperature

The coolant temperature is recorded by the coolant temperature sensor (B11/17), on model 448.8 by the coolant temperature sensor (B11/21). The signal is read in and evaluated directly by the CDI control unit (N3/33) or ME-SFI [ME] control unit (N3/34). The CDI control unit (N3/33) or ME-SFI [ME] control unit (N3/34) sends the "Coolant temperature" signal via chassis CAN (CAN E), electronic ignition lock unit (EZS) control unit (N73) and interior CAN (CAN B) to the automatic air conditioning (AAC) control unit (N154). The value is used to control the blend air flaps and to actuate the heater coolant circulation pump (M13/3).

Evaporator temperature

To prevent the evaporator from icing up, the evaporator temperature is measured by the evaporator temperature sensor (B10/5). The signals of the evaporator temperature sensor (B10/5) are read in directly by the automatic air conditioning (AAC) control unit (N154). If the evaporator temperature drops to approx. 2 °C, the A/C compressor with magnetic clutch (A9/10) is switched off.

Refrigerant pressure

The refrigerant pressure is recorded by the refrigerant pressure sensor (B12). The signal of the refrigerant pressure sensor (B12) is read in directly by the automatic air conditioning (AAC) control unit (N154). The pressure is compared with a stored temperature/pressure curve. At a refrigerant pressure of less than 0.8 bar or greater than 30 bar, the A/C compressor with magnetic clutch (A9/10) is switched off or not activated.

At a refrigerant pressure of greater than 0.8 bar and less than 30 bar, the A/C compressor with magnetic clutch (A9/10) 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 in the humidity sensor/light sensor/rain sensor/sun sensor (B38/3). The signal acquisition and actuation module (SAM) control unit (N10/1) reads in the "Sun sensor" signal over the roof LIN (LIN B13) and sends the "Solar radiation" signal over the interior CAN (CAN B) to the automatic air conditioning (AAC) control unit (N154). In the event of one-sided solar radiation, an appropriate temperature difference is set between the left and the right specified control temperatures.

Vehicle speed

The vehicle speed is sent by the Electronic Stability Program (ESP) control unit (N30/4) over the chassis CAN (CAN E), electronic ignition lock (EZS) control unit (N73) and the interior CAN (CAN B) to the automatic air conditioning (AAC) control unit (N154). The vehicle speed is used for internal calculation of the outside temperature.

Door status

The status of the respective door is determined by the following control units:

 Left front door control unit (N69/3)

 Right front door control unit (N69/4)

The respective control unit sends the "Door rotary tumbler switch" status over the interior CAN (CAN B) to the automatic air conditioning (AAC) control unit (N154). If the door is open, the automatic air conditioning (AAC) control unit (N154) retains the current blower output in order to avoid unnecessary readjustment in the event of large temperature differences between the interior air and outside air.

Settings on FRONT heater/air conditioning operating unit switch (S98/1)

The climate control settings for the driver and front passenger compartment can be adjusted using the following buttons on the FRONT heater/air conditioning operating unit switch (S98/1):

 Left temperature selection button (S98/1s1)

 Air distribution button (S98/1s2)

 Blower setting button (S98/1s3)

 "AUTO" button (S98/1s4) (with code HH4 (THERMOTRONIC automatic air conditioning))

 Defrosting button (S98/1s5)

 Climate control "MENU" and residual heat "REST" button (S98/1s6)

 Rear window heater button (S98/1s7)

 A/C button (S98/1s8) (with CODE HH9 (Semi-automatically controlled air conditioning, TEMPMATIC))

 Air recirculation mode button (S98/1s9)

 Rear heater/rear air conditioning button (S98/1s10) (with code HZ7 (Semi-automatically controlled A/C, TEMPMATIC in rear))

 Right temperature selection button (S98/1s11)

 Stationary heater button (S98/1s12) (with code H12 (Auxiliary water heater))

The settings are sent by the FRONT heater/air conditioning operating unit switch (S98/1) over the climate control LIN (LIN B8) to the automatic air conditioning (AAC) control unit (N154) where they are then processed. The data are used to regulate the air volume, air distribution and temperature. The selected settings are shown on the Audio/COMAND display control unit (A40/8).

The selected settings are sent by the automatic air conditioning (AAC) control unit (N154) over the interior CAN (CAN B), electronic ignition lock (EZS) control unit (N73), chassis CAN (CAN E), gateway for the user interface CAN (N93/4) and the user interface CAN (CAN HMI) to the radio (Audio/COMAND) (N87/6). The radio (Audio/COMAND) (N87/6) generates the corresponding picture data and sends the switch-on request over the telematics CAN (CAN A) to the Audio/COMAND display control unit (A40/8). The picture data are sent over the low voltage differential signal (LVDS) line to the Audio/COMAND display control unit (A40/8).

Settings on REAR heater/air conditioning operating unit switch (S98/2) (with code HZ7 (Semi-automatically controlled A/C, TEMPMATIC in rear))

The settings for the rear compartment climate control can be set using the buttons on the REAR heater/air conditioning operating unit switch (S98/2):

 REAR temperature selection button (S98/2s1)

 REAR blower button (S98/2s2)

The settings are sent by the REAR heater/air conditioning operating unit switch (S98/2) over the climate control LIN (LIN B8) to the automatic air conditioning (AAC) control unit (N154) where they are then processed. The data is used to regulate the air volume and temperature for the rear compartment, depending on the front compartment.

Settings on radio (Audio/COMAND) (N87/6)

The air conditioning system can be switched off or the air conditioning functions selected using the menu in the radio (Audio/COMAND) (N87/6). The control signals are sent by the radio (Audio/COMAND) (N87/6) over the user interface CAN (CAN HMI), gateway for user interface CAN (N93/4), chassis CAN (CAN E), electronic ignition lock (EZS) control unit (N73) and the interior CAN (CAN B) to the automatic air conditioning (AAC) control unit (N154).

The radio (Audio/COMAND) (N87/6) generates the corresponding picture data and sends a switch-on request over the low voltage differential signal (LVDS) line to the Audio/COMAND display control unit (A40/8).

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 (M2)

 Function sequence for actuation of the air ducting flaps

 Function sequence for actuation of A/C compressor with magnetic clutch (A9/10)

 Function sequence for actuation of electric fan (M91)

 Function sequence for actuation of PTC heater booster control unit (N33/4)

 Function sequence for actuation of heater coolant circulation pump (M13/3)

Function sequence for actuation of blower motor (M2)

Ventilation is achieved using the blower motor (M2). The automatic air conditioning (AAC) control unit (N154) sends the request over the climate control LIN 1 (LIN B8-1) to the blower regulator, which then actuates the blower motor (M2).

 The blower motor (M2) is switched off in the event of an accident.

Function sequence for actuation of the air ducting flaps

The setting of the air ducting flaps regulates the air distribution in the vehicle interior.

Function sequence for actuation of A/C compressor with magnetic clutch (A9/10)

The A/C compressor with magnetic clutch (A9/10) is responsible for intake and compression of the refrigerant. Using the A/C compressor magnetic clutch (A9/10s1), the A/C compressor with magnetic clutch (A9/10) can be completely disconnected from the power flow of the belt drive.

The automatic air conditioning (AAC) control unit (N154) regulates the A/C compressor with magnetic clutch (A9/10) directly. The A/C compressor with magnetic clutch (A9/10) then actuates the A/C compressor regulating valve (A9/10y1) and the A/C compressor magnetic clutch (A9/10s1) directly. The output of the A/C compressor with magnetic clutch (A9/10) is continuously regulated up to 100 % through the A/C compressor regulating valve (A9/10y1) by the automatic air conditioning (AAC) control unit (N154).

The automatic air conditioning (AAC) control unit (N154) also sends the idle speed increase request via interior CAN (CAN B), electronic ignition lock (EZS) control unit (N73) and chassis CAN (CAN E) to the CDI control unit (N3/33) or ME-SFI [ME] control unit (N3/34). This increases the idle speed accordingly.

 The A/C compressor with magnetic clutch (A9/10) is switched off through the A/C compressor magnetic clutch (A9/10s1) in the event of an accident.

Function sequence for actuation of electric fan (M91)

The automatic air conditioning (AAC) control unit (N154) calculates the required rotational speed for the electric fan (M91) as a function of the refrigerant pressure, and sends a request over the interior CAN (CAN B), electronic ignition lock (EZS) control unit (N73) and the chassis CAN (CAN E) to the CDI control unit (N3/33).

The CDI control unit (N3/33) or the ME-SFI [ME] control unit (N3/34) then calculates the specified fan speed as a function of the engine temperature and actuates the electric fan (M91) accordingly.

Function sequence for actuation of PTC heater booster control unit (N33/4)

The PTC heater booster control unit (N33/4) is activated as required by the automatic air conditioning (AAC) control unit (N154) over the climate control LIN 1 (LIN B8-1).

 The PTC heater booster control unit (N33/4) is switched off in the event of an accident.

Function sequence for actuation of heater coolant circulation pump (M13/3)

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 speed the heater coolant circulation pump (M13/3) is actuated to ensure that the flow rate required to heat up the blowby air is achieved. The heater coolant circulation pump (M13/3) is directly actuated by the automatic air conditioning (AAC) control unit (N154).

Function sequence for defroster function

Operating the Defrost button (S98/1s5) causes all air flaps with the exception of the defroster flaps and the fresh air and air recirculation flap to be closed. 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 automatic air conditioning (AAC) control unit (N154) regulates the blower regulator over the climate control LIN 1 (LIN B8-1) and this regulates the blower motor (M2) so that an ideal defrost mode is assured dependent on the vent air temperature.

The A/C compressor with magnetic clutch (A9/10) is activated in order to ensure that the vent air is dried. The air is dried and then heated up to the maximum temperature.

Function sequence for evaporator drying process

Additional function requirements for evaporator drying process:

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

 Outside temperature  20 °C

 Engine OFF

 Doors closed

 Kilometer reading more than 250 km

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

A timer is activated in the instrument cluster (IC) control unit (A1/1) when the engine is switched off. The "Engine running" status is sent by the CDI control unit (N3/33) or ME-SFI [ME] control unit (N3/34) via chassis CAN (CAN E), gateway for user interface CAN (N93/4) and user interface CAN (CAN HMI) to the instrument cluster (IC [KI]) control unit (A1/1).

After a waiting time of one hour, the instrument cluster (IC) control unit (A1/1) sends the request for evaporator drying over the user interface CAN (CAN HMI), gateway for the user interface CAN (N93/4), chassis CAN (CAN E), electronic ignition lock (EZS) control unit (N73) and the interior CAN (CAN B) to the automatic air conditioning (AAC) control unit (N154), which initiates evaporator drying. For this, the blower motor (M2) is actuated at the lowest stage for 30 minutes.

The automatic air conditioning (AAC) control unit (N154) sends the request over the climate control LIN 1 (LIN B8-1) to the blower regulator. The blower regulator actuates the blower motor (M2) at the lowest stage. The air supply serves to reduce residual moisture in the evaporator.

Function sequence for residual heat utilization (with CODE HH4 (THERMOTRONIC automatic climate control))

Additional function requirement for residual heat utilization function sequence:

 Circuit 15 OFF

Operating the "MENU" button for the climate control and "REST" for the residual heat (S98/1s6) on the FRONT heater/air conditioning operating unit switch (S98/1) switches on the function. The signal is read in directly over the climate control LIN (LIN B8) by the automatic air conditioning (AAC) control unit (N154). This then actuates the heater coolant circulation pump (M13/3) directly. The heater coolant circulation pump (M13/3) then pumps the still warm coolant (residual heat) through the heater heat exchanger.

The automatic air conditioning (AAC) control unit (N154) sends the "Blower motor" request at the same time over the climate control LIN 1 (LIN B8-1) to the blower regulator. The blower regulator then actuates the blower motor (M2) with low power. The air drawn in by the blower motor (M2) is routed past the heater heat exchanger and as it does so, it is heated up. The function is terminated after 30 minutes or when the on-board electrical system voltage drops below the specified value.

Function sequence for shutoff of air conditioning after an accident (crash signal sent)

To prevent the ingress of noxious gases into the vehicle interior in the event of an accident, the automatic air conditioning (AAC) control unit (N154) starts the following activities after receiving the crash signal:

 The blower motor (M2) is no longer actuated. Air is not circulated in the vehicle interior

 The fresh air and air recirculation flap is moved to the recirculated air position. Outside air can no longer enter the vehicle interior

 The A/C compressor magnetic clutch (A9/10s1) is opened. The A/C compressor with magnetic clutch (A9/10) is no longer driven

 The PTC heater booster control unit (N33/4) is switched off

The supplemental restraint system (SRS) control unit (N2/18) sends the "Crash" signal over the chassis CAN (CAN E), electronic ignition lock (EZS) control unit (N73) and the interior CAN (CAN B) to the automatic air conditioning (AAC) control unit (N154).