Rear Window Heating, Basic Function - GF67.29-P-9900A
Model all (CAR)
Overview
This document contains the following information:
- General
- Function requirement
- Heat rear window
- Shutoff conditions
General
The rear window heater heats the rear window. This allows ice or snow on the rear window to be defrosted and counteracts fogging of the rear window. Depending on the vehicle, the rear window heater is actuated by the central control unit or the rear central control unit.
When the rear window heater is switched on, the outside mirror heating is also activated.
Function requirement
- Circuit 15 ON (except pre-entry climate control for hybrid, electric vehicles)
Heat rear window
The rear window heater can be operated manually via the rear window heater switch on the air conditioning control panel and via the voice control system (VCS). The function of the rear window heater is indicated visually.
The rear window heater is automatically activated/deactivated during the pre-entry climate control (hybrid, electric vehicles) or in order to reach the operating temperature of the combustion engine more quickly. The automatically activated rear window heater is not indicated visually.
In vehicles with combustion engines, the actuation of the rear window heater is interrupted or not permitted while the engine is being started.
The duty cycle of the rear window heater is stored in the system.
Depending on the outside, interior, and coolant temperature and the vehicle speed, this varies between 2 and 26 min.
| Variable | Duty cycle | Additional information |
| - | 15 min | Normal duty cycle |
| Outside temperature above 50°C | 2 min | To protect the rear window |
| After start: Coolant temperature < operating temperature |
Maximum 15 min | Only with combustion engines, to increase the engine load |
| Outside temperature between 5 and -7°C | +30 s added to the normal duty cycle for each 1°C below 5°C | Down to -7°C corresponds to a maximum of +6 min |
| Outside temperature below 0°C at 60 km/h | +1 min added to the determined duty cycle | - |
| Outside temperature below 0°C at 70 km/h | +2 min added to the determined duty cycle | - |
| Outside temperature below 0°C at 80 km/h | +3 min added to the determined duty cycle | - |
| Outside temperature below 0°C at 90 km/h | +4 min added to the determined duty cycle | - |
| Outside temperature below 0°C at 100 km/h | +5 min added to the determined duty cycle | At a temperature of -7°C, the maximum duty cycle is thus 26 min |
Shutoff conditions
The rear window heater is deactivated by the energy management via the consumer reduction in the case of undervoltage of the on-board electrical system.
In vehicles with a combustion engine, the rear window heater is switched off when the combustion engine is switched off.
Special case: Traffic light stop
If circuit 15R remains on after the combustion engine has been switched off, the actuation of the rear window heater is interrupted for a certain amount of time. This time is stored in the system and can be adjusted via the vehicle diagnosis system. If the ignition is switched on within the stored time, the rear window heater is activated for the duty cycle that remained before the interruption. After the stored time has passed, the rear window heater must be switched on again as necessary.
| Function schematics | |||
| Function schematic, heat rear window | Model 118, 177, 247 | PE67.29-P-2500-97A | |
| Model 167 Model 293 | PE67.29-P-2500-97B | ||
| Further basic functions | |||
| Reduce consumers, basic function | GF54.10-P-1011A | ||
| Heating of mirror glass of outside mirror, basic function | GF88.79-P-1001A | ||
| Control units | |||
| Central controller unit, basic function | Model 118, 177, 247 | GF54.21-P-9895A | |
| Rear central controller unit basic function | Model 167 Model 293 |
GF54.21-P-9897A | |
| Components | |||
| Rear window heater, basic function | GF67.29-P-2006A |