GF67.29-P-0003GI Rear Window Defroster (RWD), Function

GF67.29-P-0003GI Rear Window Defroster (RWD), Function
- as of 1.12.99

Function prerequisites:
- Circuit 61 ON (engine operation recognition)
- Voltage not too low

Function
The rear window defroster is switched on when the rear window defroster switch (S21s9) in the center console is pressed.
The switch contact connects the corresponding input of the extended activity module (EAM) (N10/1) to ground when actuated.

The extended activity module (EAM) (N10/1) checks if the function prerequisites are fulfilled and switches on the rear window defroster relay (F1k1) and the rear window defroster indicator lamp (S21e2) in the rear window defroster switch (S21s9). The rear window defroster indicator lamp (S21e2) is a light diode which is connected to ground by the extended activity module (EAM) (N10/1).

Since the rear window defroster (R1) also fulfills the long wave (LW) radio antenna function the entire heating current flows over the antenna splitter (A2/5). The antenna splitter (A2/5) consists of an electric filter which separates the heating circuit from the antenna signal.

The rear window defroster relay (F1k1) connects one input of the antenna splitter (A2/5) directly to circuit 30 via a fuse.

The right antenna coil (L13/1) and the left antenna coil (L13/2) are parts of the long-wave antenna through which the heating current of the rear window defroster flows.

RF interference suppression
Malfunctions in the vehicle electrical system occurring, for example, when the rear window is switched on and off, are suppressed by the electrolytic capacitor (rear window interference suppressor) (C3).

The right antenna coil (L12/1) and the left antenna coil (L12/2) prevent the high frequency signals in the antenna system from reaching the electrical wiring in the vehicle electrical system.

Time characteristics
The extended activity module (EAM) (N10/1) switches the rear window defroster relay (F1k1) off again when
- the rear window defroster switch (S21s9) is actuated again,
- the vehicle voltage is too low or
- the maximum switch-on time is expired.

The delay time up to the automatic switch-off of the rear window defroster depends on the
- vehicle speed and
- outdoor temperature.

The precise conditions can be obtained from the reference table below.