AAC [KLA] pushbutton control unit function

P83.40-2501-04

1 Blower switch

2 Left temperature selector

3 Right temperature selector

4 Air distribution switch

N22 AAC [KLA] control and operating unit

N22b1 In-car temperature sensor

 Defroster button

 REC pushbutton

 Auto button

 EC button

 Rest button (combined with the
EC button)

Function

The AAC pushbutton control unit (N22) makes it possible to make adjustments coming from the driver such as:

 Temperature by setting the left (2) and right (3) temperature selectors

 air quantity, by adjusting the blower switch setting (1)

 air distribution, by setting the air distribution switch (4)

 air recirculation mode by pressing recirculating air pushbutton (  )

 Defrost function by pressing the defroster pushbutton
(  )

 activating the residual engine heat utilization system with the ignition switched off by pressing the rest button

(  ) (only in vehicles with code (450) taxi version and code (670a) residual engine heat utilization system MRA as of 01.06.01)

 switching off the cooling by pressing the EC button (  )

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The control unit integrated in the automatic air conditioning pushbutton (AAC) control unit (N22) looks after all system regulation and control functions such as:

 harmonizing the temperatures preselected and actually present and controlling the air outlet temperature at the air vents.

 Automatic switchover from fresh air to air recirculation mode

 Electrical control of refrigerant compressor

 Operating the engine/AC electric suction fan with integrated control

The AAC pushbutton control unit (N22) has a diagnostic capability. Consequently, any faults which occur are stored in the fault memory which can be read with the help of the diagnosis assistant system (DAS).

When replacing the AAC control and operating unit (N22) a variant coding must be conducted with the aid of the Diagnosis Assistance System (DAS).

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The AAC pushbutton control unit (N22) continues to perform the following system actuations:

 via the CAN-Class B: refrigerant compressor; in-car temperature sensor; coolant circulation pump; electric suction fan engine, AC with integrated control and rear window heater

 via AAC BUS: blower regulator; 6 stepper motors for air distribution

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The following sensor signals are read in by the AAC pushbutton control unit (N22):

 direct: Evaporator temperature sensor

 via the CAN Class B: outside temperature display temperature sensor; refrigerant pressure and temperature sensor

 via the overhead control panel control unit: in-car temperature sensor

 via the electronic ignition switch control unit: battery voltage; coolant temperature sensor; engine speed

 via the instrument cluster: vehicle speed

 via the AAC BUS: air humidity sensor

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The AAC control and operating unit (N22) reads in the window, door and tilting/sliding roof positions, in order to achieve a better control quality at the open position.

The averaged value of the interior temperature with a window open, door open and ground speed = 0 km/h is also recorded for

a maximum of 2 min. This ensures that the air conditioning system continues operating immediately with the set interior specified temperature.

The following sensor signal is transmitted by the AAC control and operating module (N22) via the CAN class B:

 Dew point temperature (the front door control units read in this value in order to ensure heating of the outside mirrors in line with demand)

The following system settings, which were activated before the engine was switched off, are stored by the AAC control and operating module (N22) in the electronic ignition switch control unit.

 EC mode activated (yes/no)

 Central automatic mode activated (yes/no)

When the engine is restarted, the status stored in the EIS control unit is reactivated.