Ventilation system, function

P83.10-2659-75

Air outlets in passenger compartment

General function requirements

 Circuit 15

General ventilation system

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/air recirculation 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) (without code (581) Comfort automatic air conditioning) or on the comfort AAC [KLA] control and operating unit (N22/7) (with code (581) Comfort automatic air conditioning), the air is directed through the air ducts and air outlets into the vehicle interior compartment.

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 In order to prevent window fogging,
the defroster vent flaps and the fresh air/air recirculation flap are closed and the footwell flaps are fully opened t = 2 min after circuit 15 has been switched off. After starting the engine, the defroster vent flaps and the footwell flaps remain in this fixed position for t = 30 s. The fresh air/air recirculation flap can be adjusted immediately. After that, all adjustments are possible again.

The ventilation system comprises the following subfunctions:

 AC component actuation function sequence

 Fresh air mode function sequence

 Air recirculation mode function sequence

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AC component actuation function sequence

The AC component actuation function sequence comprises the following subfunctions:

 Function sequence, actuation of blower motor (A32m1)

 Function sequence, actuation of the air ducting flaps

Function sequence, actuation of blower motor

Ventilation is achieved with the aid of the blower motor. The control and operating unit transmits an actuation of 0 to 100 % to the blower regulator via the AC bus (A32n1). Depending on the control voltage, the blower regulator regulates the operating voltage for the blower motor from U = 0 V up to U = 12 V and thus the rotational speed of the blower motor from 0 up to
100 %.

The actuation (operating voltage) of the blower motor is influenced by the following factors:

- Blower selector wheel setting (MANUAL/AUTO)

- Operating functions

- Mode (heating/cooling)

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- Coolant temperature

- Vehicle speed

- Solar radiation

- Fresh air/air recirculation flap position

- Flap positions

- Circuit 15 (blower ON), circuit 50 (starter running, blower off)

The blower output can be increased to match the outside temperature.

To keep the inside temperature constant and the windows clear at low temperatures, the blower output is increased by 15 % at outside temperatures of T = -10 °C to -15 °C.

Air ducting flaps actuation function sequence

The air distribution in the vehicle interior is controlled by corresponding adjustment of the air duct flaps in the air conditioning housing.

The control and operating unit then actuates the following components via the AC bus accordingly.

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Vehicles without code (581) Comfort automatic air conditioning:

- for fresh air/air recirculation control:

- Fresh air/air recirculation flap actuator motor (M2/5)

- for temperature control:

- Left blend air flap actuator motor (M2/6)

- Right blend air flap actuator motor (M2/7)

- for ventilation control:

- Left and right footwell flaps actuator motor (M2/15)

- Left and right defroster flaps actuator motor (M2/16)

- Air flaps actuator motor (M2/21)

Vehicles with code (581) Comfort automatic air conditioning:

- for fresh air/air recirculation control:

- Fresh air/air recirculation flap actuator motor

- Activated charcoal filter flap adjustment motor (A32m2)

- for temperature control:

- Left blend air flap actuator motor

- Right blend air flap actuator motor

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- for ventilation control:

- Left defroster flap actuator motor (M2/8)

- Right defroster flap actuator motor (M2/9)

- Left footwell flap actuator motor (M2/10)

- Right footwell flap actuator motor (M2/11)

- Left air flap actuator motor (M2/19)

- Right air flap actuator motor (M2/20)

Fresh air mode function sequence

The fresh air and recirculated air flap is open and fresh air is delivered into the vehicle interior through the air conditioner housing.

Additional function requirements for air recirculation mode

 Window closed

 Refrigerant compressor (A9) switched on, for automatic air recirculation mode function

 Defrost mode not active, for automatic air recirculation mode function

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Air recirculation mode function sequence

A distinction is made between the following air recirculation operating modes:

- Manual air recirculation mode via the air recirculation switch (N22s2) (without code (581) Comfort automatic air conditioning) or the air recirculation switch (N22/7s2) (with code (581) Comfort automatic air conditioning)

- Automatic air recirculation mode
(pollution-controlled air recirculation mode) (with code (581) Comfort automatic air conditioning)

Manual air recirculation mode:

When the air recirculation switch on the control and operating unit is pressed for t < 1.5 s, the fresh air/air recirculation flap is closed, and thus the supply of outside air is prevented.

The air only circulates in the vehicle interior and unpleasant odors and harmful gases are kept out.

The LED in the air recirculation switch comes on.

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When the air recirculation switch is pressed for t > 1.5 s, the windows and the panoramic roof (with code (413) Panoramic glass sunroof with top sliding sunroof) are automatically closed.

When the air recirculation switch is pressed again for t > 1.5 s, the windows and the panoramic roof return to their previous positions.

 The detailed convenience recirculation closing procedure is described in the convenience feature function (KFB).

Automatic air recirculation mode
(pollution-controlled air recirculation mode):

The comfort automatic air conditioning multifunction sensor (B31) transmits the outside air pollutant values via the AC bus to the control and operating unit. Starting from a certain pollutant concentration, the fresh air/air recirculation flap is automatically set to the recirculated air position. Outside air supply is prevented and only the inside air is recirculated.

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If the condition for pollution-controlled air recirculation mode exists after the engine is started,

a fresh air supply is first provided for t = 30 s. After that, operation continues with 80 % pollutant-controlled recirculated air and after another t = 10 s, as required, with 100 % pollutant-controlled recirculated air.

The pollutant-controlled air recirculation mode is not displayed via the function LED.