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Climate Control Regulation, Function - GF83.40-S-2012TRB

Model 447.6/7 

With Code HH4 (THERMOTRONIC automatic climate control) 

Model 447.6/7 

With Code HH9 (Air conditioner, automatic heater control) 

Model 447.6/7 

With Code HZ7 (TEMPMATIC semi-automatic air conditioning in rear) 

Model 448.7 

With Code HH4 (THERMOTRONIC automatic climate control) 

Model 448.7 

With Code HZ7 (TEMPMATIC semi-automatic air conditioning in rear) 

G16502049Courtesy of MERCEDES-BENZ USA

Shown On Model 447.6/7 (With Engine 622, 651) 

Function requirements, general 

For cooling operation:

IMPORTANT The status of circuit 15 is sent by the electronic ignition lock (EZS) control unit (N73) over the interior CAN (CAN B) to the control and operating unit (front & rear AAC) (S98). The CDI control unit (N3/33) or CDI control unit (N3/36) or MESFI [ME] control unit (N3/34) (with engine 274) sends the "Engine running" signal via chassis CAN (CAN E), electronic ignition lock (EZS) control unit (N73) and interior CAN (CAN B) to the air conditioning control and operating unit (front & rear AAC) (S98).

Climate control, general 

Climate control is provided by the signals recorded by the air conditioning control and operating unit (front & rear AAC) (S98) (e.g. interior temperature, outside temperature, coolant temperature, vehicle speed) and depending on the settings selected on the air conditioning control and operating unit (front & rear AAC) (S98).

The climate control regulation function encompasses the following subfunctions:

Function sequence for recording and evaluating signals 

The following signals are recorded and evaluated:

Outside temperature 

The signal acquisition and actuation module (SAM) control unit (N10/1) reads in the signals from the outside temperature sensor (B14) directly, uses them to calculate the outside temperature and sends this over the interior CAN (CAN B) to the air conditioning control and operating unit (front & rear AAC) (S98). The air conditioning control and operating unit (front & rear AAC) (S98) requires this value to reach the desired 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. The outside temperature is therefore only included in the control if the vehicle speed is greater or equal to 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 air conditioning control and operating unit (front & rear AAC) (S98) sends a request over the climate control LIN1 (LIN B8-1) to the blower with interior air 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 air conditioning control and operating unit (front & rear AAC) (S98) reads in the interior temperature value directly.

Temperature at left and right footwell air vents (With Code HH4 (THERMOTRONIC automatic climate control)) 

The temperature at the footwell air vents in the vehicle are recorded by the footwell air vent temperature sensors. The signals from the temperature sensors are read in directly by the air conditioning control and operating unit (front & rear AAC) (S98). The air conditioning control and operating unit (front & rear AAC) (S98) regulates the air outlet temperature at the respective air outlets.

Temperature and moisture on windshield 

The temperature and relative air humidity (dew point temperature) on the inside of the windshield is recorded by the humidity sensor/light sensor/rain sensor/sun sensor (B38/3) or the humidity sensor/light sensor/rain sensor (B38/2).

The humidity sensor/light sensor/rain sensor/sun sensor (B38/3) or the humidity sensor/light sensor/rain sensor (B38/2) sends the "Dew point sensor" signal (humidity sensor) 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 air conditioning control and operating unit (front & rear AAC) (S98). The air conditioning control and operating unit (front & rear AAC) (S98) uses the dew point temperature to calculate the relative air humidity and the temperature of the inside of the windshield.

Fogging of the windshield can thus be detected and if the windshield threatens to fog up, corresponding countermeasures are taken such as switching on the A/C compressor with magnetic clutch (A9/10).

Coolant temperature 

The coolant temperature is recorded by the coolant temperature sensor (B11/17), on model 448.7 by the coolant temperature sensor (B11/21). The "Coolant temperature sensor" signal is read in and evaluated directly by the CDI control unit (N3/33) or CDI control unit (N3/36) or ME-SFI [ME] control unit (N3/34). The CDI control unit (N3/33) or CDI control unit (N3/36) or ME-SFI [ME] control unit (N3/34) sends the "Coolant temperature" signal via chassis CAN (CAN E), electronic ignition lock (EZS) control unit (N73) and interior CAN (CAN B) to the air conditioning control and operating unit (front & rear AAC) (S98). 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 are read in directly by the air conditioning control and operating unit (front & rear AAC) (S98). 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 air conditioning control and operating unit (front & rear AAC) (S98). The pressure is compared with a stored temperature/pressure curve. At a refrigerant pressure of less than 0.8 bar and 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 or 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), evaluates it and sends the "Solar radiation" signal over the interior CAN (CAN B) to the air conditioning control and operating unit (front & rear AAC) (S98). 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 air conditioning control and operating unit (front & rear AAC) (S98). The vehicle speed is used for controlling for the internal calculation of the outside temperature, e.g. during operation while at a standstill.

Door status 

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

The respective control unit then sends the "Door rotary tumbler switch" status over the interior CAN (CAN B) to the air conditioning control and operating unit (front & rear AAC) (S98). When the door is opened, the air conditioning control and operating unit (front & rear AAC) (S98) maintains the current blower output to avoid any necessary readjustment where there are large temperature differences between the interior air and the outside air.

Settings on air conditioning control and operating unit (front & rear AAC) (S98) (With Code HH4 (THERMOTRONIC automatic air conditioning)) 

The settings for the climate control of the driver and front passenger compartment can be configured using the following buttons and selector wheels (equipment-specific) on the air conditioning control and operating unit (front & rear AAC) (S98):

The settings are processed by the air conditioning control and operating unit (front & rear AAC) (S98) whereupon the air volume, air distribution and temperature are controlled. The selected settings are indicated through LEDs in the air conditioning control and operating unit (front & rear AAC) (S98) or in the A/C operating unit display (S98p1).

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) 

Ventilation is achieved using the blower motor (M2). The air conditioning control and operating unit (front & rear AAC) (S98) sends the request over the climate control LIN 1 (LIN B8-1) to the blower regulator, which then actuates the blower motor (M2).

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

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.

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. This in turn enables additional fuel savings to be made.

The air conditioning control and operating unit (front & rear AAC) (S98) actuates 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 air conditioning control and operating unit (front & rear AAC) (S98).

In addition, the air conditioning control and operating unit (front & rear AAC) (S98) sends the request for idle speed increase 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 CDI control unit (N3/36) or ME-SFI [ME] control unit (N3/34). This increases the idle speed in accordance with the additional load that occurs when the A/C compressor with magnetic clutch (A9/10) is switched on.

IMPORTANT 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 electric fan (M91) is used for cooling the coolant and the refrigerant. The air conditioning control and operating unit (front & rear AAC) (S98) calculates the specified fan speed as a function of the refrigerant pressure and sends a 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 CDI control unit (N3/36) or ME-SFI [ME] control unit (N3/34).

The CDI control unit (N3/33) or CDI control unit (N3/36) or ME-SFI [ME] control unit (N3/34) then calculates the specified fan speed as a function of the engine temperature and directly actuates the electric fan (M91) accordingly.

Function sequence for actuation of PTC heater booster control unit (N33/4) (With Code HZ0 (Electric auxiliary heater)) 

The PTC heater booster control unit (N33/4) is switched on when required by the air conditioning control and operating unit (front & rear AAC) (S98) over the climate control LIN 1 (LIN B8-1).

IMPORTANT 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 actuated directly by the air conditioning control and operating unit (front & rear AAC) (S98).

Function sequence for defroster function 

When the defroster button (S98s4) 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 air conditioning control and operating unit (front & rear AAC) (S98) actuates the blower regulator over the climate control LIN 1 (LIN B8-1) and this actuates the blower motor (M2) so that optimum defrost operation is assured depending 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:

To counteract evaporator odors in the vehicle interior and fogging of windows when starting the air conditioning or climate control, 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 CDI control unit (N3/36) or ME-SFI [ME] control unit (N3/34) via chassis CAN (CAN E) 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 chassis CAN (CAN E), electronic ignition lock (EZS) control unit (N73) and the interior CAN (CAN B) to the air conditioning control and operating unit (front & rear AAC) (S98), which then initiates evaporator drying. For this, the blower motor (M2) is actuated at the lowest stage for 30 minutes.

The air conditioning control and operating unit (front & rear AAC) (S98) 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:

The function is switched on when the "REST" residual heat button (S98s3) on the air conditioning control and operating unit (front & rear AAC) (S98) is pressed. The air conditioning control and operating unit (front & rear AAC) (S98) 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 air conditioning control and operating unit (front & rear AAC) (S98) 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 a certain value.

Function sequence for shutting off A/C or climate control after an accident (crash signal sent) 

To prevent the ingress of noxious gases into the vehicle interior in the event of an accident, the air conditioning control and operating unit (front & rear AAC) (S98) starts the following activities after receiving the crash signal:

The 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 air conditioning control and operating unit (front & rear AAC) (S98).

  Electrical function schematic for climate control input signals Model 448.7 with code HH4 (THERMOTRONIC automatic climate control) PE83.40-S-2056-97VDC
    Model 447.6/7 with code HH4 (THERMOTRONIC automatic climate control) PE83.40-S-2056-97TRC
    Model 447.6/7 with code HH9 (Air conditioner, automatic heater control) PE83.40-S-2056-97TRD
  Electrical function schematic for climate control actuation Model 448.7 with code HH4 (THERMOTRONIC automatic climate control) PE83.40-S-2057-97VDC
    Model 447.6/7 with code HH4 (THERMOTRONIC automatic climate control) PE83.40-S-2057-97TRC
    Model 447.6/7 with code HH9 (Air conditioner, automatic heater control) PE83.40-S-2057-97TRE
  Overview of system components for climate control   GF83.40-S-9994TRB 
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