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

WARNING: This page does not describe the selected car, but rather 23 other vehicles, including the 2023 Mercedes-Benz E63 S AMG, 2023 Mercedes-Benz E53 AMG, 2023 Mercedes-Benz E350, 2022 Mercedes-Benz E53 AMG, and 2022 Mercedes-Benz E350. However, it is still accessible from the selected car via links, so may be relevant.

Model 213

up to model year 2021

with code 1U6 (R744 refrigerant)

Courtesy of MERCEDES-BENZ USA

Courtesy of MERCEDES-BENZ USA

Function requirements, general

For regulating the climate control:

Terminal 15 ON
Automatic air conditioning switched on

For cooling operation:

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

For evaporator drying process:

Engine Off

For the residual heat utilization (with code 228 (Stationary heater) or code 581 (Automatic air conditioning) or code 965 (Taxi/rental car preinstallation)):

Terminal 15 Off or terminal 15C Off

The electronic ignition lock control unit sends the status of terminal 15 via interior CAN to the A/C control unit.

The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" signal over the drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and the interior CAN to the climate control control unit.

Climate control, general

The climate control control unit regulates the temperature and the air distribution in the vehicle interior to match the settings made and the variables recorded by the various sensors (e.g. interior temperature, outside temperature, coolant temperature, vehicle speed). Appropriate settings can be made on the climate control operating unit, on the rear A/C system operating unit (with code 581 (Automatic air conditioning), or via the head unit.

The climate control control unit is networked to the vehicle electronics over the interior CAN, climate control LIN 1, climate control LIN 2, climate control LIN 3 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
Safety shutoff
Shift point adjustment (transmission 725)
Fresh air mode
Recirculated air mode
Defrost
Evaporator drying
Residual heat utilization (with code 228 (Stationary heater) or code 581 (Automatic air conditioning) or code 965 (Taxi/rental car preinstallation))

Recording and evaluation of variables

The following variables are recorded and evaluated:

Outside temperature
Interior temperature in head area
Temperature at the air outlets in the vehicle
Temperature and moisture on windshield
Coolant temperature
Evaporator temperature
Refrigerant pressure
Refrigerant temperature
Solar radiation
CO ₂ concentration level in vehicle interior
Air quality (with CODE 581 (Automatic air conditioning))
Vehicle speed
Engine speed
Door status
Position of side windows
Position of sliding roof (with code 414 (Sliding roof)) or panoramic sliding sunroof (with code 413 (Panoramic sliding sunroof))
Operating settings
Status of the voice control system (VCS [SBS]) (with code 531 (COMMAND APS))

Outside temperature

The outside temperature is recorded by the outside temperature sensor. The front SAM control unit directly reads in the outside temperature sensor signals, calculates the outside temperature and sends the data to the climate control control unit via interior CAN. The climate control control unit regulates the interior temperature according to the outside temperature by adjusting the blend air flaps.

If the vehicle is stationary, the measured temperature can differ considerably from the actual outside temperature. The outside temperature is only considered for regulation of the interior temperature if the vehicle speed is higher than 30 km/h for at least 30 s. At speeds < 30 km/h and when the ignition is switched off and on, the temperature value last measured is used.

Interior temperature in head area

The interior temperature in the head area is recorded by the interior temperature sensor with the integrated fan that is incorporated into the overhead control panel control unit. The integrated fan of the interior temperature sensor draws the air for temperature measurement out of the vehicle interior. The overhead control panel control unit reads in the value of the interior temperature and transmits this via the interior CAN to the climate control control unit.

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

Temperature and moisture on windshield

A humidity and temperature sensor is integrated in the rain/light sensor with additional functions. This sensor measures the relative air humidity and temperature directly at the inside of the windshield.

These values are used by the rain/light sensor with additional functions to calculate the dew point temperature. Comparison of the windshield surface temperature with the dew point temperature enables impending fogging of the windows to be detected.

The rain/light sensor with additional functions sends the dew point temperature via the rain/light sensor LIN, front SAM control unit and interior CAN to the climate control control unit.

If the probability of window fogging is extremely high, the climate control unit increases the blower speed. If the automatic ECO start/stop function is active, the climate control control unit can prevent an automatic engine stop. In the case of impending window fogging during an engine stop phase, the climate control control unit can cause the engine to start and the refrigerant compressor to switch in.

Coolant temperature

The coolant temperature is calculated by the CDI control unit or by the ME-SFI [ME] control unit. The CDI control unit or the ME-SFI [ME] control unit sends the coolant temperature via the drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and interior CAN to the climate control control unit.

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

Evaporator temperature

The temperature at the evaporator is recorded by the evaporator temperature sensor. The A/C control unit reads in the signals from the evaporator temperature sensor directly. If the evaporator temperature falls below 2°C, the air conditioning control unit reduces the power of the refrigerant compressor down to the shutdown. This serves to prevent the evaporator from icing up. From evaporator temperature of 2°C, the climate control control unit switches on the refrigerant compressor again.

The evaporator temperature is kept at 2°C for max. 30 min. The evaporator temperature is then adjusted to a range between 3 and 8°C (depending on the cooling output requirement).

Refrigerant pressure

The refrigerant pressure is recorded by the CO₂ pressure/temperature sensor upstream of the gas cooler. The climate control control unit directly reads the signals of the CO₂ pressure/temperature sensor upstream of the gas cooler. The pressure is compared with a stored temperature/pressure curve. At a refrigerant pressure of less than 24 bar or more than 140 bar, the climate control control unit switches off the refrigerant compressor, or it does not switch it on.

Refrigerant temperature

The refrigerant temperature upstream of the gas cooler is recorded by the CO₂ pressure/temperature sensor upstream of the gas cooler. The refrigerant temperature downstream of the gas cooler is recorded by the CO₂ pressure/temperature sensor downstream of the gas cooler. The comparison of both values enables the gas cooler function to be monitored. The climate control control unit directly reads in the signals from the CO₂ pressure/temperature sensors.

Solar radiation

A sun sensor (2-quadrant sensor) is integrated in the rain/light sensor with additional functions. The sun sensor detects the angle of incidence and the intensity of the solar radiation entering the left and right side of the vehicle. The rain/light sensor with additional functions sends this information via the rain/light sensor LIN, front SAM control unit and interior CAN to the climate control control unit. The climate control control unit then regulates the interior temperature accordingly. For example, in the event of one-sided solar radiation, an appropriate temperature difference is set between the left and the right specified control temperatures.

If the sun shines into the vehicle from the side or from the rear and additionally at an acute angle, the sun sensor delivers imprecise values. For this reason, a sun sensor is emulated virtually in the rear. Location information is obtained from GPS data. The position of the sun is deduced from the time of day. The head unit sends the relevant information via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the climate control control unit. The climate control control unit references the values from the sun sensor at the windshield and adapts the temperature control accordingly.

CO ₂ concentration level in vehicle interior

The CO₂ concentration in the vehicle interior is recorded by the CO₂ sensor. The CO2 sensor sends corresponding information over the climate control LIN 3 to the climate control control unit. To match the CO₂ concentration level in the vehicle interior, the climate control control unit supplies fresh air or switches off the A/C system. Appropriate warnings are shown on the instrument cluster.

Detailed information on the safety strategy is available in the "Safety shutoff" chapter.

Air quality (with CODE 581 (Automatic air conditioning))

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

Carbon monoxide (CO)
Nitrogen oxides (NO_x )

The climate control control unit reads in the signals from the air quality sensor via the climate control LIN 1. If the concentration of pollutant gas is high, the climate control control unit activates air recirculation mode.

Vehicle speed

The vehicle speed is calculated by the instrument cluster. Information about the vehicle speed is transmitted by the instrument cluster via the user interface CAN, the electronic ignition lock control unit and the 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 calculated by the CDI control unit or the ME-SFI [ME] control unit. The CDI control unit or the ME-SFI [ME] control unit sends the engine speed via the drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and interior CAN to the climate control control unit. The engine speed is used to regulate the refrigerant compressor, among other things.

Door status

The status of each door (open or closed) is determined by the following control units and sent via the interior CAN to the climate control control unit:

Left front door control unit
Right front door control unit
Left rear door control unit
Right rear door control unit

If the door is open, the climate control control unit references the values from the interior temperature sensor with integrated fan 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.

Position of side windows

The position of the side windows is determined by the following control units and sent via the interior CAN to the climate control control unit:

Left front door control unit
Right front door control unit
Left rear door control unit
Right rear door control unit

If the side windows are open, the climate control control unit references the values from the interior temperature sensor with integrated fan 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.

Position of sliding roof (with code 414 (Sliding roof)) or panoramic sliding sunroof (with code 413 (Panoramic sliding sunroof))

The position of the sliding roof is transmitted by the sliding roof control module to the A/C control unit via the interior CAN. The position of the panoramic sliding sunroof is transmitted by the panoramic sliding sunroof control unit to the A/C control unit via the interior CAN.

If the sliding roof or panoramic sliding sunroof is open, the climate control control unit references the values from the interior temperature sensor with integrated fan 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
Rear air conditioning operating unit (with code 581 (Automatic air conditioning))
Head unit
VCS (with code 531 (COMMAND APS))

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
Climate control and residual heat ON/OFF menu button (with code 228 (Stationary heater) or code 581 (Automatic air conditioning))
Right temperature selection button
Left air distribution button (with CODE 581 (Automatic air conditioning))
"SYNC" button (with code 580 (Air conditioning) or code 965 (Taxi/rental car preinstallation))
"A/C" button (with code 580 (Air conditioning) or code 581 (Automatic air conditioning) except code 228 (Stationary heater))
Right air distribution button (with CODE 581 (Automatic air conditioning))
"A/C" and residual heat ON/OFF button (with code 965 (Taxi/rental car preinstallation))
Blower button, front
AUTO button, front
Defrosting button
Air distribution button (with code 580 (Air conditioning) or code 965 (Taxi/rental car preinstallation))
"OFF" button and climate control menu (with code 580 (Air conditioning) or code 965 (Taxi/rental car preinstallation))

The climate control operating unit sends information regarding the settings via the climate control LIN to the climate control control unit. This data is used to regulate the air flow, air distribution and interior temperature. The selected settings are additionally displayed on the Audio/COMMAND display. For this purpose, the climate control control unit sends the relevant information via the interior CAN, the electronic ignition lock control unit and the user interface CAN to the head unit. The head unit generates the corresponding image data, transmits a switch-on request via the telematics CAN to the audio/COMMAND display and transfers the image data via the HSVL line to the audio/COMMAND 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.

The air conditioning system or the refrigerant compressor can be switched off if the "A/C" button, the "OFF" button and the climate control menu or the "A/C" and residual heat ON/OFF button is installed. If these buttons are not installed, it can be switched off via the menu in the head unit.

Rear air conditioning operating unit (with code 581 (Automatic air conditioning))

Settings for climate control in the rear compartment can be made at the rear air conditioning operating unit. The rear air conditioning operating unit sends information regarding the settings via the climate control LIN to the climate control control unit. This data is used to regulate the air volume and the temperature in the rear compartment. The settings are shown in the display of the rear air conditioning operating unit.

Head unit

You can switch off the air conditioning system, or select the air conditioning functions using the menu in the head unit. The head unit sends the relevant information via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the climate control control unit. The head unit generates the corresponding image data, transmits a switch-on request via the telematics CAN to the audio/COMMAND display and transfers the image data via the HSVL line to the audio/COMMAND display.

VCS (with code 531 (COMMAND APS))

The following functions of the air conditioning system can be operated via voice input using the VCS [SBS]:

Switching the air conditioning system on and off, or switching the refrigerant compressor on and off
Switching synchronization function on or off (with code 580 (air conditioning system) or code 965 (Taxi/rental car preinstallation))
Switching ionization on or off (with code P21 (Air quality package))
Switching on or off, or setting the perfume atomizer (with CODE P21 (Air quality package))
Switching defrost function on or off
Switching automatic climate control on or off
Switching air-recirculation mode on/off
Setting the climate control settings (with code 581 (Automatic air conditioning))
Setting the interior temperature
Setting the air distribution
Setting the air flow

The VCS [SBS] is integrated into the head unit. The head unit sends the relevant information via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the climate control control unit.

Status of the VCS (with code 531 (COMMAND APS))

When the VCS is active, the output of the electronic blower motor is limited by the climate control control unit. The head unit sends the status of the VCS over the user interface CAN, electronic ignition lock control unit and the interior CAN to the A/C control unit.

Actuation of air conditioning components

Actuation of the air conditioning components encompasses the following subfunctions:

Actuation of electronic blower motor
Actuation of electronic booster blower (with code 581 (Automatic air conditioning))
Actuation of air ducting flaps
Actuation of refrigerant compressor
Actuation of CO ₂ expansion valve
Actuation of fan motor (engine fan)
Actuation of PTC heater booster (engine 654, 642 or 274 with code 401 (Seat climate control for driver and front passenger) or code 824 (Additional parts for cold countries) or code 873 (Seat heater for driver and front passenger) or code 902 (Seat heater plus for driver and front passenger) except code 228 (Stationary heater) or code 913 (Hot country code))
Actuation of coolant circulation pump
Actuation of driver side air vent ionizer (with code P21 (Air quality package))
Actuation of perfume atomizer generator (with code P21 (Air quality package))

Actuation of electronic blower motor

Ventilation of the vehicle interior is achieved with the aid of the electronic blower motor. The climate control control unit actuates the electronic blower motor via climate control LIN 2.

The electronic blower motor drives a radial blower which circulates the air in the vehicle interior or supplies fresh air to the vehicle interior. This prevents the windows from fogging up, supplies air to the vehicle occupants and allows pleasant and constant temperatures to be reached quickly in the vehicle interior. Depending on the current settings at climate control operating unit, the air is distributed via various air ducts and air outlets in the vehicle interior.

Model 213

up to model year 2021

with code 1U6 (R744 refrigerant)

with code 531 (COMMAND APS)

With VCS [SBS] active, the blower setting is reduced.

The electronic blower motor is switched off in the event of an accident (crash signal transmitted).

Actuation of electronic booster blower (with code 581 (Automatic air conditioning))

The electronic booster blowers improve ventilation of the rear compartment. The climate control control unit actuates the electronic booster blowers via climate control LIN 2. Actuation takes place depending on the settings made at the rear air conditioning operating unit.

If the electronic booster blowers are switched on, the electronic blower motor is also actuated.

The electronic booster blowers are switched off following an accident (crash signal sent).

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 components are actuated by the A/C control unit via climate control LIN 1:

Vehicles with CODE 580 (Air conditioning):

Right blend air flap via the right blend air flap actuator motor (temperature control)
Rear blend air flap over the rear blend air flap actuator motor (temperature control)
Left footwell/center air vent/side air vent and rear air vent flap via the left footwell/center air vent/side air vent and rear air vent flap
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)
Fresh air/ram air/air recirculation flap over fresh air/ram air/air recirculation flap actuator motor (fresh air/ram air/air recirculation control)
Defroster/footwell/center air vent flap over defroster/footwell/center air vent flap actuator motor (ventilation control)
The position of the defroster/footwell/center air vent flap is detected by the central air distribution position detection microswitch. The climate control control unit reads in the status of the central air distribution position detection microswitch directly.

Vehicles with CODE 581 (Automatic air conditioning):
Left blend air flap via left blend air flap actuator motor (temperature control) actuator motor (ventilation control)
Right footwell/center air vent and side air vent flap via the right footwell/center air vent and side air vent flap actuator motor (ventilation control)
Fresh air/ram air/air recirculation flap over fresh air/ram air/air recirculation flap actuator motor (fresh air/ram air/air recirculation control)
Defroster flap via the defroster/footwell/center air vent flap actuator motor (ventilation control)
Left B-pillar air distribution via left B-pillar air distribution actuator motor (ventilation control)
Right B-pillar air distribution via right B-pillar air distribution actuator motor (ventilation control)

Courtesy of MERCEDES-BENZ USA

Air outlets in vehicle interior, shown with code 580 (Air conditioning)

Model 213

up to model year 2021

with code 1U6 (R744 refrigerant)

with code 581 (Automatic air conditioning)

There are additional air outlets in the B-pillar trim.

Actuation of refrigerant compressor

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

A magnetic clutch is integrated into the refrigerant compressor's belt pulley. This magnetic clutch can be used to disconnect the refrigerant compressor completely from the power flow in the belt drive. This in turn enables additional fuel savings to be made. The climate control control unit directly regulates the refrigerant compressor magnetic clutch.

The output of the refrigerant compressor is continuously regulated up to 100 % by the climate control control unit using the refrigerant compressor regulating valve. The A/C system control unit actuates the refrigerant compressor regulating valve directly.

In addition, the climate control control unit sends the calculated torque of the refrigerant compressor via the interior CAN, electronic ignition lock control unit, chassis FlexRay, powertrain control unit and drivetrain CAN to the CDI control unit or 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.

The refrigerant compressor is switched on under the following conditions:

Refrigerant pressure over 26 bar
Refrigerant pressure below 93 bar
Refrigerant temperature upstream of gas cooler under 160°C

The refrigerant compressor is not switched on or switched off under the following conditions:

Refrigerant pressure below 24 bar (switch-on interlock for lack of refrigerant)
Refrigerant pressure over 95 bar (switch-on interlock when static pressure too high)
Refrigerant pressure over 140 bar (shutoff at overpressure)
Refrigerant temperature upstream of gas cooler over 170°C (shutoff at overtemperature)

As from a refrigerant pressure of 133 bar or a refrigerant "temperature of 165°C, the output of the refrigerant compressor is governed by the actuator current.

In the event of an accident (crash-signal sent), the refrigerant compressor is disconnected from the belt drive by the refrigerant compressor magnetic clutch.

Actuation of CO2 expansion valve

The CO₂ expansion valve restricts the flow of refrigerant and relieves it into the evaporator in a targeted manner.

The climate control control unit actuates the CO ₂ expansion valve over the climate control LIN 3. The opening angle of the CO₂ expansion valve can thereby be continuously adjusted between 13 and 100 %.

Actuation of fan motor (engine fan)

The fan motor is used for cooling the coolant and refrigerant. The climate control control unit calculates the target fan speed according to the refrigerant pressure and temperature, and sends it via the interior CAN, electronic ignition lock control unit, chassis FlexRay, powertrain control unit and engine CAN to the CDI control unit or to the ME control unit.

The CDI control unit or the ME-SFI [ME] control unit corrects the requested target fan speed to match the engine temperature and actuates the fan motor accordingly.

Actuation of PTC heater booster (engine 654, 642 or 274 with code 401 (Seat climate control for driver and front passenger) or code 824 (Additional parts for cold countries) or code 873 (Seat heater for driver and front passenger) or code 902 (Seat heater plus for driver and front passenger) except code 228 (Stationary heater) or code 913 (Hot country code))

When required, the PTC heater booster is switched on by the A/C control unit over the climate control LIN 2. As a result, the vehicle interior is heated up more quickly.

The PTC heater booster is switched off in the event of an accident (crash signal transmitted).

Actuation of coolant circulation pump

The coolant circulation pump supports the coolant circuit. The heated coolant passes through the heater heat exchanger, which dissipates heat to the air blowing by. At low engine rpm or at engine stop, 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.

Additional function requirements for actuation of driver side air vent ionizer (with CODE P21 (Air quality package))

Ionization activated
Blower switched on
Climate control active

Actuation of driver side air vent ionizer (with code P21 (Air quality package))

The driver side air vent ionizer is used for ionization of the air in the vehicle interior. The air is cleaned and freshened by means of ionization. The ionization of the interior air itself is odor-neutral and cannot be detected directly as such in the vehicle.

The head unit transmits the "Switch on ionization" request via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the climate control control unit. The A/C control unit actuates the driver side air vent ionizer via climate control LIN 2.

Additional function requirements for actuation of perfume atomizer generator (with CODE P21 (Air quality package))

Perfume atomization activated
Glove compartment CLOSED
Flask inserted
Climate control active

The status of the glove compartment (open or closed) is sensed by the glove compartment lamp switch. The perfume atomizer alternator directly reads in the status of the glove compartment switch.

Actuation of perfume atomizer generator (with code P21 (Air quality package))

The perfume atomizer generator is used to supply fragrance to the vehicle interior. A fan is installed in the fragrance generator, which produces a flow of purified air. When the vial is inserted and the perfume atomization has been switched on, the air flow is guided over the surface of the fragrance and enriched with scent molecules. This scented air is delivered directly into the vehicle interior through an opening in the diffuser grid (in front of the Audio/COMMAND display) and diffuses throughout the vehicle. Perfume atomization is pulsed, i.e.it is active for 5min after activation and then switches itself off for 5 min. The interval switching is used to prevent the vehicle occupants from getting used to the scent. This maintains the occupants' perception capability of the perfume atomization.

The head unit transmits the "Switch on perfume atomization" request and the "Perfume atomization intensity" request via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the A/C control unit. The A/C control unit actuates the perfume atomizer alternator via climate control LIN 2.

The glove compartment lamp switch sends a ground signal directly to the perfume atomizer generator when the glove compartment is opened. It then switches off active perfume atomization and switches the flask illumination on. The flask in the perfume atomizer generator is also disconnected from the working position and moved to the removal position.

When the glove compartment is closed, the inserted flask is moved to the working position by the perfume atomizer generator with terminal 15 on. The perfume atomizer generator also switches off the flask illumination and activates the last perfume atomization intensity set in the climate control menu of the head unit.

If no flask is inserted in the perfume atomizer generator, the message "Insert perfume atomizer cartridge" appears in the Audio/COMMAND display. The perfume atomizer generator recognizes whether a flask was inserted by measuring the power consumption of the integrated motor. If another object is used instead of the flask, the perfume atomizer generator can recognize the object as a flask by mistake.

Safety shutoff

To enable appropriate measures to be initiated in the event of any leakage in the refrigerant circuit early on, the CO2 concentration level in the vehicle interior is continuously monitored. The CO2 refrigerant is denser than air and drops to the floor in the event of any leakage. The health hazard effect of CO2 therefore lies in the displacement of oxygen. If a leakage is detected, the climate control control unit starts the active ventilation of the vehicle interior (active scavenging process). Different warnings are also shown on the instrument cluster. To this end, the climate control control unit sends the corresponding request over the interior CAN, electronic ignition lock control unit and the user interface CAN to the instrument cluster.

At a CO₂ concentration level of more than 5, 000 ppm when driving, the climate control control unit starts the fresh air mode or partial air recirculation mode function (where air recirculation mode was previously in use).
The air recirculation mode is not enabled again until the CO₂ concentration level of 5, 000 ppm is undershot.
At a CO₂ concentration level of more than 10, 000 ppm when driving, the climate control control unit starts active ventilation. The climate control control unit activates the fresh air mode, blower setting 2 and the footwell air distribution.
These measures are only canceled once the CO₂ concentration level drops to less than 5, 000 ppm.
At a CO₂ concentration level of more than 25, 000 ppm when driving, the climate control control unit starts active ventilation.
The climate control control unit activates the fresh air mode, blower setting 2 and the footwell air distribution. The "A/C system malfunction, see operator's manual" warning message is also shown on the instrument cluster and a warning tone emitted. These measures are only canceled once the CO₂ concentration level drops to less than 5, 000 ppm.
At a CO₂ concentration level of more than 25, 000 ppm over a time period of 5 minutes when driving, the climate control control unit starts the active ventilation process.
The climate control control unit activates the fresh air mode, at least blower setting 2 and the footwell air distribution. The "Malfunction, supply vehicle interior with fresh air, Service Required" warning is also shown in red in the instrument cluster and a warning tone emitted. These measures are only canceled once the CO2 concentration level drops to less than 25, 000 ppm.
At a CO2 concentration level of more than 25, 000 ppm while parking, the climate control control unit is woken up.
The climate control control unit starts the active ventilation and activates the fresh air mode, blower setting 2 and the footwell air distribution. The "Malfunction, supply vehicle interior with fresh air, Service Required" warning is also shown in red in the instrument cluster and a double warning tone emitted. The double warning tone is repeated 60 times.

These measures are only canceled once the CO2 concentration level drops to less than 5000 ppm.
When the accuracy of the sensors is reduced, the climate control control unit starts active ventilation.
The climate control control unit activates the fresh air mode, blower setting 2 and the footwell air distribution. The "A/C system malfunction, see operator's manual" warning message is also shown on the instrument cluster and a warning tone emitted. These measures are not automatically canceled and they are shown at each restart.
If the CO₂ sensor fails, the climate control control unit starts the active ventilation.
The climate control control unit activates the fresh air mode, blower setting 2 and the footwell air distribution. When driving, the "Malfunction, supply vehicle interior with fresh air, Service Required" warning is also shown in red in the instrument cluster and a double warning tone emitted. If the vehicle is parked, the "Malfunction, supply vehicle interior with fresh air, Service Required" warning is shown in red in the instrument cluster and a double warning is emitted that is repeated 60 times.

The message remains visible in the instrument cluster until the malfunction is rectified.

In order to prevent harmful gases entering the vehicle interior after an accident, the climate control control unit starts the following activities:
- The electronic blower motor is no longer actuated. The air is no longer circulated in the vehicle interior.
- The electronic blower motors are no longer actuated. The air is no longer circulated in the rear of the vehicle.
- The fresh air/ram air/recirculated air flap is moved to the recirculated air position. Outside air can no longer enter the vehicle interior.
- The refrigerant compressor magnetic clutch is opened. The belt pulley of the refrigerant compressor is no longer driven.
- The PTC heater booster is switched off (engine 654, 642 or 274 with code 401 (Seat climate control for driver and front passenger) or code 824 (Additional parts for cold countries) or code 873 (Seat heater for driver and front passenger) or code 902 (Seat heater plus for driver and front passenger) except code 228 (Stationary heater) or code 913 (Hot country code)).

The supplemental restraint system control unit transmits the crash signal via the user interface CAN, the electronic ignition lock control unit and the interior CAN to the A/C control unit.

Detailed information on actuation of the individual components in the air conditioning is available in the "Actuating the A/C components" chapter.

Shift point adjustment (transmission 725)

If increased cooling or heating is required, the fully integrated transmission control unit can adjust the shift point.

The A/C control unit sends the shift point adjustment request over the interior CAN, electronic ignition lock control unit, chassis FlexRay, powertrain control unit and the drive train CAN to the fully integrated transmission control unit.

Fresh air mode

The fresh air/ram air/air recirculation 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 air/ram air/air recirculation flap actuator motor via climate 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 (with code 581 (Automatic air conditioning))
Automatic air recirculation mode

Air recirculation mode via the air recirculation mode button

Pressing the air recirculation mode button on the climate control operating unit for longer than 1.5 s closes the fresh air/ram air/air recirculation flap to prevent air entering from the outside. The air only circulates in the vehicle interior and unpleasant odors and harmful gases are kept out. The LED in the air recirculation mode button lights up during air recirculation mode.

The climate control operating unit reads in the status of the air recirculation mode button directly and sends the status to the climate control control unit via the climate control LIN. The climate control control unit actuates the fresh air/ram air/air recirculation flap actuator motor via climate control LIN 1 and sends the "air recirculation mode active" status via climate control LIN 1 to the climate control operating unit which actuates the LED in the air recirculation mode button.

The air recirculation mode is switched off automatically:

After 5 min at outside temperatures below 5°C
After 5 min, if cooling with air dehumidification is switched off
After 30 min at outside temperatures above 5°C and if cooling with air dehumidification is switched on

Vehicles except code 460 (Canada version) or code 494 (USA version) or code 835 (South Korea vehicles additional parts): If the air recirculation mode button is pressed for > 1.5 s, the side windows and the sliding roof (with code 414 (Sliding roof)) or the panoramic sliding sunroof (with code 413 (Panoramic sliding sunroof)) are closed. If the air recirculation mode button is then pressed for > 1.5 s, the side windows and the sliding roof (with code 414 (Sliding roof)) or the panoramic sliding sunroof (with code 413 (Panoramic sliding sunroof)) are moved back to their default positions (provided that they were not manually adjusted during air recirculation mode).

Additional function requirements for pollutant-sensitive air recirculation mode (with code 581 (Automatic air conditioning))

Refrigerant compressor switched on

Pollutant-controlled air recirculation mode (with code 581 (Automatic air conditioning))

The air quality sensor sends the outside air pollutant values over the climate control LIN 1 to the A/C control unit. Starting from a certain pollutant concentration, the fresh air/ram air/recirculated air flap is automatically set to the recirculated air position. Outside air supply is prevented and only the inside air is recirculated. If the conditions for the pollutant-controlled air recirculation mode exist after the engine is started, a supply of fresh air is first provided for 30 s. Then 80 % of pollutant-controlled air recirculation mode is initially used. After 10 s, the output is increased to 100 % pollutant-controlled air recirculation mode if necessary.

The pollutant-controlled air recirculation mode is active for max. 30 min and is not indicated by the LED in the air recirculation mode button.

Additional function requirements for automatic air recirculation mode

Automatic air conditioning activated
Outside temperature above 5°C (for automatic air recirculation mode in a tunnel)

Automatic air recirculation mode

The air recirculation mode is switched on automatically:

At high outside temperatures
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.
In a tunnel (with code 531 (COMMAND APS))
The head unit sends the GPS data via user interface CAN, electronic ignition lock control unit and interior CAN to the A/C control unit.

The A/C control unit actuates the fresh air/ram air/air recirculation flap actuator motor over the climate control LIN 1 and the fresh air/ram air/air recirculation flap is set to the recirculated air position.

The automatic air recirculation mode is active for max. 30 min and is not indicated by the LED in the air recirculation mode button.

Defrost

Operating the defrosting button causes all the air flaps with the exception of the defroster flap and the fresh air/ram air/air recirculation flap to be closed. Both these flaps 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 climate control control unit actuates the electronic blower motor via climate control LIN 2 in such a way that optimum defrost operation is guaranteed depending on the outflowing air temperature.

The refrigerant compressor is activated in order to ensure that the air flowing out is dried. The air is dried and then heated up to the maximum temperature.

Additional function requirements for evaporator drying process

Refrigerant compressor was active at least once during the last ignition cycle
Evaporator temperature above 3°C
Outside temperature above 20°C
Doors closed
Kilometer reading over 250 km

Evaporator drying

To counteract odors in the vehicle interior and fogging of windows when the air conditioning system is started, evaporator drying is carried out.

After the engine is switched off, the climate control control unit sends the signal to activate the evaporator drying timer via the interior CAN, the electronic ignition lock control unit and the user interface CAN to the instrument cluster. The CDI control unit or the ME-SFI [ME] control unit sends the "Engine running" signal over the drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and the interior CAN to the climate control control unit.

After a waiting time of 1 h, the instrument cluster sends the request for evaporator drying via the user interface CAN, electronic ignition lock control unit and interior CAN to the climate control control unit, which starts the evaporator drying process. For this purpose, the electronic blower motor is actuated at the lowest stage for 30 min. The climate control control unit actuates the electronic blower motor via climate control LIN 2. The air supply serves to reduce residual moisture in the evaporator.

Residual heat utilization (with code 228 (Stationary heater) or code 581 (Automatic air conditioning) or code 965 (Taxi/rental car preinstallation))

Pressing the climate control menu and residual heat ON/OFF button (with code 228 (Stationary heater) or code 581 (Automatic air conditioning)) or the "A/C" and residual heat ON/OFF button (with code 965 (Taxi/rental car preinstallation)) on the climate control operating unit switches on the residual heat utilization function. The A/C control unit reads in the control signals of the climate control operating unit via climate control LIN and actuates the coolant circulation pump directly. The coolant circulation pump delivers the still warm (residual heat) coolant through the heat exchanger.

The climate control control unit actuates the electronic blower motor via climate control LIN 2 at the same time. The intake air from the electronic blower motor is routed past the heater heat exchanger and heated up in the process. The function is terminated after 30 min or when the on-board electrical system voltage drops below a certain value.

	Electrical function schematic for climate control input signals		PE83.40-P-2056-97DBB
	Electrical function schematic for climate control actuation		PE83.40-P-2057-97DBB
	Overview of system components for climate control		GF83.40-P-9994FG