Automatic air conditioning control and operating unit, task - GF83.40-P-2180-01PP

Shown on AAC [KLA] control and operating unit (N22) as from 1.6.02

Fig 1: Identifying Automatic Air Conditioning Control And Operating Unit - Shown On AAC [KLA] Control And Operating Unit (N22) As From 1.6.02

To regulate the automatic air conditioning (AAC [KLA]), the following tasks are performed by the AAC [KLA] control and operating unit (N22):

Synchronizing the temperatures preselected and actually present and controlling the air outlet temperature at the air outlets.
Automatic switchover from fresh air to air recirculation mode
electrical control of refrigerant compressor
operating the engine/AC electric suction fan with integrated control

In addition, the following functions are also regulated by the AAC [KLA] control and operating unit (N22) and the information required for this is sent for further processing on the Controller Area Network bus class B (interior) (CAN-B).

Heated rear window
Stationary heater (with code (228) Stationary heater)

The AAC control and operating unit (N22) is used to actuate the following:

Refrigerant compressor via CAN-B
Heating water circulation pump
Engine and AC electric suction fan with integrated control
Heated rear window
Blower regulator and all components connected to the AC bus

The following information is sent from the AAC [KLA] control and operating unit (N22) over CAN-B:

Dew-point temperature
The left front door control unit and right front door control unit read in this value, to provide for a heated outside mirror that can be regulated according to individual requirements.

The following information is read in by the AAC [KLA] control and operating unit (N22):

In-car temperature sensor (N22b1)
evaporator temperature sensor
via CAN-B:
- Outside temperature display temperature sensor
- Refrigerant pressure and temperature sensor
via EIS [EZS] control unit
- Battery voltage
- Coolant temperature sensor
- Engine speed
Via the instrument cluster:
- Vehicle speed
Via A/C bus:
- air humidity sensor

The window and door positions as well as the position of the tilting/ sliding roof (for code (414) Power glass tilting/sliding roof) are read in by the AAC [KLA] control and operating unit (N22) in order to achieve better control quality when they are open.

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 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.

AC OFF 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. The AAC push-button control unit (N22) has a diagnostic capability. As a result, any faults which occur are stored in the DTC memory, which can be read out with the aid of STAR DIAGNOSIS.

When replacing the AAC [KLA] control and operating unit (N22), a variant coding must be performed using STAR DIAGNOSIS.

Blower switch (1)

The blower switch (1) controls the output of the blower motor. The blower switch (1) sets the control voltage for the blower regulator in 6 stages and 4 intermediate settings via the AAC [KLA] control and operating unit (N22). This facilitates control of the blower speed from 0 - 100 %.

Temperature selector wheel, left (2) and right (3)

The left temperature selector wheel (2) and right temperature selector wheel (3) are used to preselect the required interior temperature. The desired interior temperature can be set separately for the left and right sides by turning the wheel. The AAC [KLA] control and operating unit (N22) compares the desired temperature with the current interior temperature, which is measured by the in-car temperature sensor (up to 31.5.02 and as of 1.6.05) in the overhead control panel control unit and additionally by the in-car temperature sensor (N22b1) on the AAC [KLA] control and operating unit (N22).

Using the comparison between specified and actual values, the AAC [KLA] control and operating unit (N22) determines the correct setting of the blend air flaps and actuates these separately. The selected temperature is reached and maintained as quickly as possible, if warming or cooling of the interior is necessary.

Air distribution switch (4)

The air distribution switch (4) controls the air flow to the air outlets for ventilation of the passenger compartment.

The air distribution can be set manually or automatically:

Manually by turning the air distribution switch (4)
Automatically by pressing the Auto button (6)

By turning the air distribution switch (4) on the AAC [KLA] control and operating unit (N22), the fresh air/air recirculation flaps actuator motor, the left blend air flap actuator motor, the right blend air flap actuator motor, the left and right footwell flaps actuator motor, the left and right defroster flaps actuator motor and the fresh air flaps actuator motor are actuated via the AC bus for air distribution.

Apart from the 4 basic settings, a further 8 intermediate settings can be selected.

Defroster button (5)

By pressing the defroster button (5), the defroster function is initiated, which operates according to the following new logic:

heating power is controlled by the outside temperature.
the entire air flow is directed at the windshield and the front side windows, and the defroster outlets are opened
the blown-in air is dehumidified depending on the humidity in reheat mode
blend air flaps controlled
footwell vents closed
blower power at 80 %, can be manually controlled

Air recirculation switch (N22s2)

Briefly pressing the air recirculation switch (N22s2) for < 1.5 s actuates the fresh/air recirculation flaps actuator motor, which actuates the fresh air/air recirculation flap; this in turn closes the fresh air duct and opens the recirculated air duct to enable air to be supplied from the vehicle interior. The LED in the air recirculation switch (N22s2) lights up during air recirculation mode.

Recirculation air convenience closing function

If the air recirculation switch (N22s2) is pressed for longer than > 1.5 s, then along with the air recirculation function all open windows and the tilting/sliding roof (SHD (for code (414) Power glass tilting/sliding roof) in automatic mode are closed (windows and tilting/sliding roof (SHD) must be normalized). The function LED in the air recirculation switch (N22s2) lights up during air recirculation mode. Tilting/sliding roof (SHD) and power windows are operated one after the other in order to avoid current peaks.

If the button is pressed once again for > 1.5 s, the windows and the tilting/sliding roof (SHD) are moved back into the previously stored position and the fresh air and air recirculation flap moves into the fresh air position (function LED in air recirculation switch (N22s2) off). The convenience closing function can only be started if the function LED in the air recirculation switch (N22s2) is not on.

Any window which has been opened manually during this recirculation air phase, remains in this position when the recirculation air function is canceled, all other windows move into the stored position.

The positions of the tilting/sliding roof (SHD) and of the side windows that existed before the start of the closing operation are stored by the overhead control panel control unit or the corresponding door control unit. The windows and the tilting/sliding roof (SHD), which were closed using the comfort closing function, remain closed, if the air recirculation button is operated for < 1.5 s. In this case only the fresh air/recirculated air flap is moved into the fresh air position. The stored positions are canceled when the ignition is switched off.

Auto button (6)

Automatic mode can be activated for the left and right sides simultaneously by pressing the Auto button (6).

In automatic mode, in addition to temperature control the blower output and air distribution are controlled automatically.

The blower speed is continuously controlled depending on the temperature difference between the specified and actual values. For electronic control of the system humidity is also used in addition to interior temperature.

AC OFF button (7)

When the AC OFF button (7) on the AAC [KLA] control and operating unit (N22) (LED on) is pressed, the refrigerant compressor is shut off and thus the cooling mode is switched off. The air is no longer cooled and dried.

In vehicles with diesel engines the heater booster control unit is also shut off. All other functions are retained. The pollutant-controlled recirculated air function is not available in AC OFF mode.

In order to shut off the refrigerant compressor, the AAC [KLA] control and operating module (N22) sends the shutoff request and specified value = 0% via the CAN class B to the front SAM control unit with fuse and relay module. At the same time, the refrigerant compressor torque is set to "0" and transferred to the engine electronics and the electronic transmission control (ETC [EGS]) via the EIS [EZS] control unit. The front SAM control unit with fuse and relay module sends the canceled load increase signal to the engine electronics via the EIS control unit and switches the refrigerant compressor off after a defined time delay.

The AC OFF button (7) is installed in the AAC [KLA] control and operating unit (N22) in vehicles up to 31.5.02 as an EC button. The EC button has the same tasks and functions as the AC OFF button (7) which has been installed as from 1.6.02.

REST button (for code (450) Taxi version or for code (670) Residual engine heat utilization system (REST [MRA]))

Pressing the REST button, which is combined with the AC OFF button (7), switches off the residual engine heat utilization system. When the engine is switched off, the residual heat heats the vehicle depending on the temperature adjustment on the AAC control and operating module (N22) and the ambient temperature in the vehicle interior. Heating can thus continue for another approx. 30 minutes.

The function is only available when the ignition is switched off or the transmitter key in the EIS [EZS] control unit is in position 1. The residual engine heat utilization system is switched off automatically in the event of undervoltage.

The flaps for the air distribution and the air volume are regulated automatically.