Ventilation system, function

P83.10-2575-05

Function requirements, general

 Circuit 15 ON

 The status of circuit 15 is sent by the electronic ignition lock control unit (N73) over the interior CAN (CAN B).

Ventilation, general

The ventilation system prevents windows from fogging up, supplies air to the vehicle occupants, and ensures that uniform and pleasant temperatures in the vehicle interior are reached quickly. When the fresh air/recirculated air flap is adjusted correspondingly, fresh air is supplied to the air conditioner housing via the air inlet. Depending on the current settings on the AAC [KLA] control and operating unit (N22/7), the air is routed into the vehicle interior through air ducts and air outlets.

 To prevent any fogging of the windows, t = 2 minutes after switching off circuit 15 the defroster flaps and the fresh air/recirculated air flap are closed. In vehicles with code (581) Comfort automatic air conditioning, the footwell flaps are also opened all the way. After starting the engine, the defroster flaps and the footwell flaps remain in this position for t = 30 s. The fresh air/recirculated air flap can be adjusted immediately. After that, all adjustments are possible again.

 At "Circuit 15 OFF" when one of the doors is opened the fresh air/recirculated air flap is opened to 50 % by the fresh air/recirculated air flap actuator motor (M2/5) and the ram air flap (with code (581) Comfort automatic air conditioning) by the ram air flap actuator motor (M2/34) (up to 31.5.10) or by the fresh air/recirculated air flap actuator motor (as of 1.6.10). This achieves a significant reduction in the door closing forces.

The function can be set with the diagnostic tester.

The ventilation encompasses the following subfunctions:

 AC component actuation function sequence

 Fresh air mode function sequence

 Air recirculation mode function sequence

 Function sequence for ram air operation

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 (A32m1)

 Function sequence for actuation of the air ducting flaps

Function sequence for actuation of blower motor

Ventilation is achieved with the aid of the blower motor. The automatic air conditioning control and operating unit forwards the request directly to the blower regulator (A32n1), which then actuates the blower motor. With code (581) Comfort automatic air conditioning, the ventilation of the rear passenger compartment is also supported by the rear blower motor (M2/1). Actuation is performed by the AAC control and operating unit over the climate control LIN (LIN B8).

 With an active voice control system (VCS [SBS]) the blower output is limited. To this end, the radio with auto pilot system (A2/56) (with code (511) Audio 50 APS with DVD changer) or the COMAND controller unit (A40/3) (with code (512) COMAND APS with DVD changer or with code (527) COMAND APS with single DVD drive (with navigation)) sends the VCS status over the interior CAN to the AAC control and operating unit. This then limits the blower output.

 In vehicles with code (B03) ECO start/stop function, the blower output is restricted when the engine is stopped.

The CDI control unit (N3/9) (with diesel engine) or ME-SFI [ME] control unit (N3/10) (with gasoline engine) sends the "Engine stop" status over the chassis CAN (CAN E), front SAM control unit with fuse and relay module (N10/1) and the interior CAN to the AAC control and operating unit. The AAC control and operating unit then restricts the blower output.

 In vehicles as of 1.6.13, the blower motor and with code (581) Comfort automatic air conditioning, the rear blower motor is switched off after an accident.

Function sequence for actuation of the air ducting flaps

The air distribution in the vehicle interior is controlled by corresponding adjustment of the air duct flaps in the air conditioning housing. The automatic air conditioning control and operating unit actuates the following components over the climate control LIN:

Vehicles without code (581) Comfort automatic air conditioning:

 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 (M2/6) (temperature control)

 Right blend air flap via right blend air flap actuator motor (M2/7) (temperature control)

 Defroster flap via the defroster flap actuator motor (M2/16) (ventilation control)

 Air distribution flap via the air distribution flap actuator motor (M16/22) (ventilation control)

Vehicles with code (581) Comfort automatic air conditioning:

 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)

 Rear blend air flap via the rear blend air flap actuator motor (M235) (temperature control)

 Left defroster flap via the left defroster flap actuator motor (M2/8) (ventilation control)

 Right defroster flap via the right defroster flap actuator motor (M2/9) (ventilation control)

 Left footwell flap via the left footwell flap actuator motor (M2/10) (ventilation control)

 Right footwell flap via the right footwell flap actuator motor (M2/11) (ventilation control)

 Left center air vent flap via the left center air vent flap actuator motor (M2/12) (ventilation control)

 Right center air vent flap via the right center air vent flap actuator motor (M2/13) (ventilation control)

 Diffuser flap via the diffusor flap actuator motor (M2/21) (ventilation control)

 Ram air flap (up to 31.5.10) via the ram air flap actuator motor (ram air control)

 Fresh air/recirculated air flap (as of 1.6.10) via the fresh air/recirculated air flap actuator motor (ram air control)

 In vehicles as of 1.6.13 the fresh air/recirculated air flap is closed after an accident.

Fresh air mode function sequence

The fresh air/recirculated air flap is opened and fresh air is delivered into the interior by means of the air conditioner housing.

Air recirculation mode function sequence

The function sequence for the air recirculation mode encompasses the following subfunctions:

 Function sequence for the air recirculation mode over the air recirculation mode button (N22/7s2)

 Pollutant-controlled air recirculation mode function sequence (with code (581) Comfort automatic air conditioning)

Function sequence for air recirculation mode using air recirculation mode button

When the air recirculation mode button on the AAC control and operating unit is pressed for t < 1.5 s, the fresh air/recirculated air flap is closed, thereby impeding the supply of outside air. The air only circulates in the vehicle interior and unpleasant odors and harmful gases are kept out. The light-emitting diode (LED) in the air recirculation mode button lights up. Pressing the air recirculation mode button for t > 1.5 s activates comfort air recirculation closing. The side windows and the tilting/sliding roof (with code (414) Electric glass tilting/sliding roof) or the panoramic sliding sunroof (with code (413) Panoramic glass sunroof with top sliding sunroof) are then automatically closed. When the air recirculation mode button is pressed again for t > 1.5 s, the side windows and the tilting/sliding roof or the panoramic sliding sunroof return to their previous positions.

 The side windows and the tilting/sliding roof or the panoramic sliding sunroof, which were manually opened during the air recirculation phase, are not moved back to their previous positions once the air recirculation phase is over.

 In vehicles with code (460) Canada version and code (494) USA version, comfort recirculation closing is not possible.

 The detailed comfort air recirculation closing procedure is described in the separate convenience feature (CF [KFB]) function description.

Additional function requirements for pollutant-controlled air recirculation mode (with code (581) Comfort automatic air conditioning)

 A/C compressor (A9) switched on without code (B09) A/C compressor with magnetic clutch)

 A/C compressor with magnetic clutch (A9/7) switched on (with code (B09) A/C compressor with magnetic clutch)

 Defrost mode not active

Pollutant-controlled air recirculation mode function sequence (with code (581) Comfort automatic air conditioning)

The pollutant sensor (B31) sends the pollutant values for the outside air over the climate control LIN to the control and operating unit. Starting from a certain pollutant concentration, the fresh 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, fresh air is supplied for t = 30 s. Operation continues with 80 % pollutant-controlled recirculated air, and then, if required, with 100 % pollutant-controlled recirculated air after another t = 10 s.

 The pollutant-controlled air recirculation mode is not indicated by the LED lighting up.

Function sequence for ram air operation

Ram air operation is speed-dependent. The vehicle speed signal is sent by the instrument cluster (A1) over the interior CAN to the AAC control and operating unit. A differentiation is made in ram air mode between 2 variants:

 Vehicles without code (581) Comfort automatic air conditioning

 Vehicles with code (581) Comfort automatic air conditioning

Vehicles without code (581) Comfort automatic air conditioning

In a vehicle speed range between v = 60 km/h and v = 160 km/h the fresh air/recirculated air flap is gradually closed by the fresh air/recirculated air flap actuator motor. As from a speed of v > 160 km/h, the fresh air/recirculated air flap is closed completely.

Vehicles with code (581) Comfort automatic air conditioning

In a vehicle speed range between v = 60 km/h and v = 160 km/h, the ram air flap is closed in stages by the ram air flap actuator motor (up to 31.5.10) or by the fresh air/recirculated air flap actuator motor (as of 1.6.10). As from a speed of v > 160 km/h, the ram air flap is closed completely.