Right-Hand Operating Unit on Rear Air Conditioner

Right-Hand Operating Unit On Rear Air Conditioner

Right-hand operating unit on rear air conditioner
The right-hand operating unit on the rear air conditioner is used for individual operation of the rear air conditioner with left-right separation.
The operating unit regulates the air supply and air temperature (only cooling possible) in the rear via the right-hand roof air vent.
The left-hand operating unit on the rear air conditioner is connected directly via a plug-in connection to the righthand operating unit on the rear air conditioner. This means that all the settings for the left-hand operating unit on the rear air conditioner are picked up and digitized in the electronics of the right-hand operating unit on the rear air conditioner.

The right-hand operating unit on the rear air conditioner consists essentially of the following parts:
- Temperature dial
- Electronic module
- Button for manual variation of the air flow rate
- 5 LEDs (for display of the selected air flow rate)

Functional description
The right-hand operating unit on the rear air conditioner is activated via the LIN bus by the control unit of the automatic rear air conditioning (HKA control unit).
The locating lights are controlled via terminal 58g by the footwell module.

The signals of the following components are picked up and digitized in the electronics of the right-hand operating unit on the rear air conditioner:
- Temperature dial (right-hand operating unit on the rear air conditioner)
- Temperature dial (left-hand operating unit on the rear air conditioner)
- Button for manual variation of the air supply (right-hand operating unit on rear air conditioner)
- Button for manual variation of the air supply (left-hand operating unit on rear air conditioner)
- Roof air vent temperature sensor, left
- Roof air vent temperature sensor, right

The right-hand operating unit on the rear air conditioner sends the signals on the LIN bus to the HKA control unit. After signal evaluation, the HKA control unit activates the mixed-air flap motors, the air-distribution-flap motors, the LEDs, as well as the fan of the rear air conditioner by means of an output stage.







Structure and inner circuit
The right-hand operating unit on the rear air conditioner is connected via a 26-pin plug-in connection to the vehicle network.







Target values
Observe the following target values for the right-hand operating unit on the rear air conditioner:

Variable Value
Power supply 12 V
Voltage range 8 to 16 V
Temperature range -40 ± 85 °C

Diagnosis instructions

Failure of the component:
If the right-hand operating unit in the rear air conditioner fails, the following behavior is to be expected:
- Failure during operation:
- The current settings are retained.
If only the temperature dial or the button for manual variation of the air flow rate or both components fail, the current settings of the components concerned are retained.
If only the LED display fails, the HKA control unit can no longer activate the LEDs to indicate the selected air flow rate.
- No changes are displayed for the buttons and temperature dials in the left-hand or right-hand operating unit of the rear air conditioner.
- The HKA control unit uses a default value for both roof air vent temperature sensors (left and right).
- Fault code memory entry in the HKA control unit
- Failure is determined on starting:
- The settings on the temperature dials are signalled internally as invalid. The mixed-air flap motors as well as the air-distribution-flap motors are no longer activated. This means the flap motors remain in their parking positions.
The parking position is a certain position to which a flap motor is move after the vehicle has been stopped and parked and after a specified waiting period (stored in the memory chip of the HKA control unit). The flap motors are re-initialized to this parking position after starting up.
- The buttons for manual variation of the air flow rate are signalled internal as not pressed. This means the fan for the rear air conditioner remains off.
- The HKA control unit uses a default value for both roof air vent temperature sensors (left and right).
- Fault code memory entry in the HKA control unit

No liability can be accepted for printing or other errors. Subject to changes of a technical nature