Rear Air Conditioning Part 2

Rear Air Conditioning

Step motor control

Communication between control module and step motors: The two ventilation flaps and the two stratification flaps are adjusted by means of four bipolar step motors. In order to ensure the required torques at the flaps, the step motors are linked to the flap mechanism by reduction gears.

All step motors are connected in parallel to a three-wire flat cable connection. The three wires carry the voltage supply, ground and serial data information. The control commands are sent to the step motors across a serial data flow from the control module of the rear air conditioning.

To make each step motor unique, they are given their own addresses. Each programmed address can only be written in once and then no longer deleted or changed. This means that the step motors are not interchangeable. Each step motor operates as a "slave". The step motor "listens" to all the data on the bus, but only accepts and executes a command when its own address has been detected. Moreover, the telegram must have been transferred without errors. When the step motor executes a command, it generates a status message and returns this as a reply to the control module.

Positioning accuracy: Changes in the vehicle voltage result in different torques for the MUX4 motors. Whereas the motors are activated in lower-noise sinus operation with voltages U (BKL30) > 11 V, if the voltages are lower they must be switched to full-step operation.

Changing the activation mode:
U (BKL30) < 9.0 V motor stops
9.0 V < U (UBKL30) < 10.0 V motor runs with 140 Hz and full-step operation
10.0 V < U (BKL30) < 11.0 V motor runs with rated frequency and full-step operation
11.0 V < U (BKL30) < 16.0 V motor runs with rated frequency and sinus operation
16.0 V < U (BKL30) motor stops (due to power loss at activation IC)

These conditions also apply to the reference run!

Reference run: As none of the step motors is provided with actual position detection, they always move relative to one of the flap end positions (reference points: 0 / 100%). If a control module is replaced or the power supply is interrupted during normal operation, the flaps are forced into an end position. The end position is selected in such a way that the subsequent set point position can be reached by the shortest route possible (route optimization).

Inclusion of the nominal position here achieves optimization of the motor running time: If the flap is to remain open after the reference run, the reference run is also carried out in the "open" direction. There is route optimization according to the following criteria:

Route optimization during reference run:
- Nominal value ≥ 50% reference run in OPEN direction
- Nominal value < 50 % reference run in CLOSED direction

The reference run can also be initiated by set values of the diagnostic tester.

Position run: When the car is brought to a stop (with dropping terminal 15), the step motors move the flaps into certain positions. Here, the ventilation flaps are closed and the stratification flaps are set to their middle position.

Setting angle, number of steps and adjusting time:
- Ventilation flap, left and right:
Setting angle: 100 degrees

Number of steps: per 15 degrees = 300 steps (at 100 degrees approx. 2000 steps)

Adjusting time: CLOSED <-> OPEN approx. 10 seconds

- Stratification flap, left and right:
Setting angle: 109 degrees

Number of steps: per 15 degrees = 300 steps (at 109 degrees approx. 2180 steps)

Adjusting time: CLOSED <-> OPEN approx. 11 seconds

Operation of the rear air conditioning
The rear air conditioning can be operated from the left-hand and right-hand control panels and the button for the rear cooler box (ON / OFF). Partial operation is also possible from the IHKA.

Operation using buttons:
- MAX AC button: This button is used to set the fan to maximum power and the stratification to cold on the corresponding side.
- OFF button: This button is used to block the air supply on the corresponding side by closing the ventilation flap.

NOTE: Both sides in OFF mode switches the rear air conditioning to OFF.

- ON / OFF button on rear cooler box: This button in the lid can be used to switch the rear cooler box on and off.
However, the rear cooler box can only be operated using the button if both FKA control panels are in the OFF mode. The rear cooler box is always automatically switched on as soon as a control panel is switched to manual mode or if MAX AC is active.

Functional relationships: The functional relationships for terminal 15 ON are:







Operation via rotary actuator:
- Rotary actuator, left: This rotary actuator is used to set the desired temperature value (cooling effect / stratification) on the corresponding side.
- Rotary actuator, right: This rotary actuator is used to set the air supply manually by changing the flap opening and the fan blower speed.

Influence on OFF and MAX AC functions:
- OFF active: Moving the temperature adjuster or fan adjuster on one side by at least one increment activates the mode that was active before OFF.
- MAX AC active: Moving the temperature adjuster or fan adjuster on one side by at least one increment activates the manual mode of that side.

NOTE: "Manual mode active" is a coding option. The function is currently not coded.

- Manual mode active Moving the fan adjuster and temperature adjuster to MAX AC conditions (temperature adjuster at minimum temperature and fan at maximum power) on one side activates the MAX AC LED (but not the MAX AC program) on that side.

Operation via IHKA: Switching on MAX AC at the control panel of the IHKA switches both control panels of the FKA into the MAX AC mode.

If the MAX AC mode is switched off again at the control panel of the IHKA, the status that was set before MAX AC was switched on is recreated on both sides of the rear air conditioning. However, this sequence only applies if no adjustment was made to the FKA during the MAX AC function. Subsequently, the rear air conditioning can be operated in the normal manner.

Operation via Controller (BM front): The Control Display communicates via the K-CAN SYSTEM data bus with the rear air conditioning and can influence its settings. The following settings are possible using the Controller and displays on the Control Display:
- Rear cooler box: The rear cooler box can be switched on and off by the Controller via the Control Display if both control panels of the FKA are in OFF mode. Otherwise, the rear cooler box is generally switched on. The status of the rear cooler box is reported back to the Control Display and indicated by an LED in the button.
- Status of rear air conditioning: The rear air conditioning can be switched off by the Controller by signal change and switched into the MAX AC mode. If the change is from 0 to 1, both control panels are switched into the MAX AC mode; if the change is from 1 to 0, into the OFF mode. Following the changeover, the FKA can again be operated in the normal manner. The status of the rear air conditioning is reported back to the Control Display.

NOTE: With signal = 0, both control panels are switched off. With signal = 1, in the case of manual mode and in the MAX AC mode at least one control panel is switched on.

Display elements
Function LEDs: All button operations are indicated by the activation of function LEDs and symbol and locating light LEDs in the buttons:
- Function indicator lamp MAX AC and rear cooler box ON: green
- Function indicator lamp OFF: orange
- Symbol and locating light: orange

So that the LEDs reflect the status of the program as true feedback, all function LEDs are activated by the control module of the FKA.

The brightness of the function LEDs is kept constant by a voltage regulator. The priority of the buttons is set by a program. For priority display, the function indicator lamp of the lower-ranked button is switched off.

Day / night switching of LEDs: The brightness of the function LED is designed for daylight. In order to avoid dazzle during nighttime operation, the brightness is reduced when the lights are on and terminal 58g is active. For brightness control, the LED supply is clocked with a PWM signal. The value for the minimum brightness of the function LED is stored. The symbol LEDs are also dimmed depending in terminal 58g. The status of terminal 58g is passed on to the control system of the rear air conditioning with the K-CAN message "Dimming". The light status is transferred by the light module with the telegram "Lamp status".

Transport and workshop mode
If one of these two modes is activated, the rear air conditioning switches into the OFF mode. This status is retained as long as one of the modes is active (operation is blocked). After termination of the transport mode, the rear air conditioning remains in the OFF status, but it can be operated once again.

These modes are activated/deactivated by means of standard diagnosis telegrams.

Notes for Service department
Filling mode
For the rear air conditioning, a filling mode can be activated via the diagnosis interface. During activation, the front shut-off valve on the IHKA and the rear shut-off valve on the FKA are opened.

Calibrating the potentiometer limit values for right-hand and left-hand control panel
Manual operation of the rear air conditioning is separate on the left-hand and right-hand control panels. As only the right-hand control panel is "intelligent", it must be calibrated to the exact limit values of the potentiometer of the left-hand control panel.

Prerequisite for calibration: terminal R active, terminal 15 not active.

Starting the calibration:
- With buttons: On both control panels, simultaneously press all buttons for at least three seconds.

Following the start of the calibration, the LEDs of the OFF button and the MAX button of the left-hand control panel flash.

Default values that lie safely above the minimum values or safely below the maximum values are entered in the memory locations for the limit values of the potentiometer of the left-hand control panel.

Calibrating the potentiometers:

NOTE: The order of steps must be followed without fail. If the rotary actuators are not turned up to the limit position, a malfunction can occur (incremental adjustments are no longer registered).

1. Turn both rotary actuators to the left-hand stop (minimum values)
2. Press the MAX AC button: The MAX AC LED stops flashing as acknowledgment that the left-hand limit stops have been stored.
If the measured values are above the values that were entered in each memory location on starting, these values are not accepted and the MAX AC LED continues to flash.
3. Turn both rotary actuators to the right limit position (maximum values).
4. Press the OFF button: The OFF LED stops flashing as acknowledgment that right-hand limit stops have been stored.

If the measured values are below the values that were entered in each memory location on starting, these values are not accepted and the OFF LED continues to flash.

Reference run of the step motors (MUX motors):
The reference run of the step motors can be triggered using the diagnosis tester.

Diagnosis
The diagnostic concept consists of two parts: The self-diagnosis has the task of diagnosing faults in hardware components by means of application tasks and making the information resulting from the diagnosis available to a tester via the fault memory management. The interface between the two diagnosis sections is the data gained from the diagnosis.

Self-diagnosis:
- All inputs and outputs can be activated in the diagnostic program.
- The control module has a self-diagnosis cycle. In one cycle, the fault location (fault code), type of fault, fault counter and environment related conditions are stored.

The self-diagnosis is activated when terminal 15 is switched on. The following diagnosis conditions must be met before switching on:
- Rotation speed = 0 or engine running signal via CAN
- Vehicle voltage (terminal 30) within the operating range 11 V ... 15.5 V
- No request for independent heating / independent ventilation

The self-diagnosis is active following a system buildup time of t = > 4 seconds.

During normal operation (up to deactivation of terminal 15), a cyclical diagnosis is performed at the inputs at intervals of 4 seconds. In the case of the outputs, only a limited diagnosis is possible, as with various system outputs only the current operating status is checked for faults.

If a sporadically occurring fault is detected, the corresponding diagnosis defect bit is set in the memory of the control module. A fault is entered in the fault memory of the control module.

Fault messages are only generated if the diagnosis conditions have been met.

In the event of a fault, the defective system input is replaced by the relevant substitute value. System outputs are deactivated in the event of a fault. In the case of drivers for two outputs and a status line, the output must remain activated in certain cases, otherwise a fault is also detected for the intact output.

In the subsequent diagnostic cycle (repair attempt every 20 seconds), the fault status of the system ports is determined once again. In the event of a fault, in general a maximum of 15 repair attempts are made. Thereafter, the output is regarded as defective and is initially no longer activated in this operating cycle. The self-diagnosis is only run and another 15 repair attempts for each defective output are only made when terminal 15 has been switched to OFF and then back to ON.

Within 3 seconds of switching off the ignition (terminal 15), the fault entries are transferred from the fault memory into the memory. Coding data is stored immediately.

Following "Power on reset" (terminal 30), the memory content is transferred into the fault memory of the control module. In the fault memory, the entries (fault location and type of fault) are supplemented and/or updated according to the current fault situation.

Following the last change to the control panel settings, these settings are secured in that they are saved again:
- with the engine running, every 10 seconds
- with the engine stopped, every second

Country-specific version