GF67.29-P-0003RI Heated Rear Window, Function
GF67.29-P-0003RI Heated Rear Window, Function
Function requirements, general
^ No overvoltage or undervoltage
^ Circuit 15 On
^ Vario roof closed and locked
The status of circuit 15 is transmitted by the EIS control unit (N73) to the rear SAM control unit (N10/8) via the interior CAN. The RVC control unit also transmits the status of the Vario roof (N52) to the rear SAM control unit via interior CAN.
Heated rear window, general
Actuation of the heated rear window (R1) serves to defrost the rear window and keep it free thereby providing the driver with a clear view to the rear.
The heated rear window function comprises the following partial functions:
^ Manual on/off function sequence
^ Function sequence for operating time
^ Function sequence for consumer shutoff
^ Function sequence for switch-on delay
Manual on/off function sequence
Switch-on of the rear window heater is requested by pressing the rear window heater switch (N22s1) on the AAC control and operating unit (N22).
The AAC control and operating unit directly reads in the status of the rear window heater switch and transmits the switch-on request to the rear SAM control unit via the interior CAN. The rear SAM control unit actuates the rear window heater relay (K40/5kU) and thereby switches on the rear window heater. Actuation of the LED in the rear window heater switch signals that the rear window heater is actuated.
When the rear window heater switch is pressed again, actuation of the rear window heater is terminated, simultaneously the LED in the rear window heater switch goes out.
Function sequence for operating time
The operating time of the rear window heater is calculated by the rear SAM control unit depending on the outside temperature and the vehicle speed.
For this purpose, the signal from the outside temperature indicator temperature sensor (B14) is provided by the driver-side rear SAM control unit with fuse and relay module (N10/10) and information on the vehicle speed is provided by the instrument cluster (A1) to the interior CAN. The rear SAM control unit Fond reads in all relevant information, evaluates them and actuates the rear window heater via the rear window heater relay. The operating time of the rear window heater is t = 6 min. under normal conditions.
At outside temperatures of T < 5 °C the operating time is extended by t = 30 s per 1 °C drop in temperature up to a maximum of t = 6 min. (corresponds to T = -7 °C).
At outside temperatures of T < 0 °C the operating time of the rear window heater is extended with increasing vehicle speed.
Additional duty cycle depending vehicle speed:
- v > 60 km/h, t = 1 min.
- v > 70 km/h, t = 2 min.
- v > 80 km/h, t = 3 min.
- v > 90 km/h, t = 4 min.
- v > 100 km/h, t = 5 min. (maximum value)
Function sequence for consumer shutoff
If, during the heating phase, the rear SAM control unit recognizes a undervoltage of U ≤ 10.5 V or an overvoltage of U ≥ 17 V for min. t = 70 ms, the rear window heater switches off. The LED in the rear window heater switch is flashing at a frequency of H = 1.5 Hz. If the on-board power supply voltage stabilizes to a normal value of U ≥ 11.6 V ≤ 15 V within t = 30 s, the heated rear window is switched on automatically and the LED is actuated permanently.
However, if the voltage is too low or too high for longer than t = 30 s, the rear window heater is switched off completely. It must then be switched back on again manually.
Function sequence for switch-on delay
At lower outside temperatures (T < -10 °C) switch-on of the rear window heater is delayed to reduce the load on the on-board electrical system until the passenger compartment is slightly heated (T = 5 °C).
However, the LED in the rear window heater switch is actuated immediately so that the driver is not irritated.
The interior temperature is sensed by the in-car temperature sensor (N70b1) in the overhead control panel control unit (N70). The overhead control panel control unit reads in the signals from the in-car temperature sensor and transmits them to the rear SAM control unit via the interior CAN.
