Rear window heater, function - GF67.29-P-3002GN
MODEL 166 as of model year 2016
MODEL 292
Function requirements, general
- Terminal 15 ON
- No undervoltage or overvoltage
- Consumer shutoff not active
The electronic ignition lock control unit transmits the status of circuit 15 over the interior CAN to the automatic air conditioning control and operating unit.
Rear window heater, general
If the rear window heater is active, the heated outside mirror is always active as well.
The rear window heater function comprises the following partial functions:
- Manual on/off function sequence
- Function sequence for automatic switch-on
- Function sequence for determining operating time
- Function sequence for traffic light stop
- Consumer shutoff function sequence
Manual on/off function sequence
The rear window heater is switched on and off with the rear window heater button in the automatic air conditioning control and operating unit.
The automatic air conditioning control and operating unit directly reads in the status of the rear window heater button and then actuates the rear window heater via the rear window heater relay. The automatic air conditioning control and operating unit directly actuates the LED in the rear window heater button.
The rear window heater function is terminated when the rear window heater button is pressed again. The LED goes out simultaneously.
Function sequence for automatic switch-on
To reach the operating temperature of the engine more quickly, the rear window heater is switched on to max. t = 15 min. to increase the engine load. In this case the LED in the rear window heater button does not confirm by flashing.
The CDI control unit (diesel engine) or the ME-SFI [ME] control unit (gasoline engine) sends the switch-on request via chassis CAN 1, electronic ignition lock control unit and interior CAN to the automatic air conditioning control and operating unit. The automatic air conditioning control and operating unit then actuates the rear window heater via the rear window heater relay. On model 166.063, the ME-SFI [ME] control unit sends the switch-on request via drive train CAN, powertrain control unit, chassis CAN 1, electronic ignition lock control unit and interior CAN to the automatic air conditioning control and operating unit.
The rear window heater function can also be switched on or off using the pre-entry climate control function (model 166.063).
MODEL 166.063 as of model year 2016
Detailed information about the preairconditioning function is contained in the separate partial function "Preairconditioning function".
Function sequence for determining operating time
The operating time of the rear window heater is stored in the automatic air conditioning control and operating unit. Depending on the outside temperature, inside temperature and vehicle speed, it is t = 2 to t = 26 min.
The outside temperature is recorded by the outside temperature sensor. The SAM control unit directly reads in the signal of the outside temperature sensor, calculates the outside temperature and sends it to the instrument cluster over the interior CAN. The outside temperature displayed is transmitted by the instrument cluster to the automatic air conditioning control and operating unit via interior CAN.
The interior temperature is recorded by the interior temperature sensor with integrated fan in the overhead control panel control unit. The SAM control unit reads in the interior temperature via roof LIN and transmits this via interior CAN to the climate control control and operating unit. The vehicle speed is transmitted by the instrument cluster to the automatic air conditioning control and operating unit via the interior CAN.
The duty cycle is as follows:
- The normal duty cycle is t = 15 min.
- At outside temperatures of T < 5 °C, the duty cycle is extended by t = 30 s per 1 °C drop in temperature, up to a maximum of t = 6 min (this corresponds to an outside temperature of T = -7 °C).
- At outside temperatures of T < 0 °C, a speed-dependent time factor is also taken into consideration.
The following times are added up for the operating time during the heating phase dependent on the vehicle speed:
- Vehicle speed v > 60 km/h: t = 1 min
- Vehicle speed v > 70 km/h: t = 2 min
- Vehicle speed v > 80 km/h: t = 3 min
- Vehicle speed v > 90 km/h: t = 4 min
- Vehicle speed v > 100 km/h: t = 5 min (maximum value)
At outside temperatures of T > 50 °C, the switch-on time of the rear window heater is limited to t = 2 min to protect the rear window.
Function sequence for traffic light stop
If the engine is switched off when the rear window heater is activated (function requirement circuit 15R ON), the automatic air conditioning control and operating unit switches the rear window heater off. The operating time is not decreased. If, within t = 5 min. c. 15 is not switched back on, the rear window heater is reactivated.
After expiration of the traffic light stop time without switching on circuit 15, the rear window is switched off completely.
The traffic stop light time can be parameterized with the diagnosis tester in the automatic air conditioning control and operating with range t = 0 min to t = 10 min. During engine start, the rear window heater is switched off momentarily. The rear window heater is switched back on t = 10 s after the engine is started.
Consumer shutoff function sequence
To ensure on-board electrical system stability during all driving cycle phases, the SAM control unit continuously evaluates the voltage in the on-board electrical system. When overload situations occur, the automatic air conditioning control and operating unit scales back the rear window heater or switches it off (on-board electrical system management). The consumer shutoff request is sent by the SAM control unit via the interior CAN to the automatic air conditioning control and operating unit.
The operating time is not decreased. The LED in the rear window heater remains switched on.
If the on-board electrical system voltage was stabilized again within t = 5 minutes, the automatic air conditioning control and operating unit switches the rear window heater back on. The rear window heater is then operated for the remaining operating time.
However, if the consumer shutoff lasts longer than t = 5 min., the LED of the rear window heater button is also switched off. For this purpose the front SAM control unit transmits the status of the consumer shutoff to the automatic air conditioning control and operating unit via the interior CAN.
If the consumer shutoff continues and the rear window heater button is pressed again, the LED in the rear window heater button comes on for t = 1.5 s and then goes out.
The rear window heater can only be reactivated, when the energy management for the consumer shutoff has canceled the switch-off.
Detailed information about the consumer shutoff function is provided in the "Energy management function" description.
PRE-SAFE® function:
If the seat belts in the vehicle have to be tensioned as part of the PRE-SAFE® function, the rear window heater is switched off if it was previously switched on.
For this purpose, the Electronic Stability Program control unit sends a signal via chassis CAN 1, the electronic ignition lock control unit and the interior CAN to the SAM control unit. The SAM control unit then starts consumer shutoff. The automatic air conditioning control and operating unit then switches off the rear window heater function.
| Function schematic for electrical rear window heater | PE67.29-P-2051-97NBA |
| Overview of system components for climate control | GF83.40-P-9994GN |