Rear Window Defogger

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NOTE:

If there is a condition preventing the rear window defogger to be switched on (short circuit in the connection to the Rear Window Defogger Relay -J9-, open circuit in the voltage supply to the Comfort System Central Control Module -J393-, etc.), this is stored as a malfunction in the Comfort System Central Control Module -J393- and the information is sent via the data bus/Data Bus On Board Diagnostic Interface -J533- to the front Air Conditioning (A/C) display control head, the Climatronic Control Module -J255- indicating that the event memory in the Comfort System Central Control Module -J393- must be read out see Vehicle Diagnostic Tester in the "Guided Fault Finding " function. The activation of the Rear Window Defogger -Z1- is displayed in the measured value of the Comfort System Central Control Module -J393-, refer to Vehicle Diagnostic Tester in the "Guided Fault Finding ".

If the voltage at terminal "30" measured at the Vehicle Electrical System Control Module -J519- falls below a value stored in the Vehicle Electrical System Control Module -J519- or the front A/C display control head, the Climatronic Control Module -J255-, the rear window defogger is switched off completely (or the power is reduced), therefore reducing the load on the Generator -C- Vehicle Diagnostic Tester in the "Guided Fault Finding " function.

If the activation of the Rear Window Defogger -Z1- must be switched off due to insufficient voltage, the indicator lamp in the rear window defogger switch in the front A/C display control head, the Climatronic Control Module -J255-, remains on. However, if the deactivation lasts longer than approx. 100 seconds, the Climatronic Control Module -J255- switches the indicator lamp off.

The "read measured values" function of the Guided Fault Finding of the front A/C display control head, the Climatronic Control Module -J255-, displays the fact that the rear window defogger is switched on or why activation did not occur despite a request see Vehicle Diagnostic Tester in the "Guided Fault Finding " function.

The function test for the activation of the rear window defogger is described in the Guided Fault Finding for the Comfort System Central Control Module -J393- see Vehicle Diagnostic Tester in the "Guided Fault Finding " function.

The duration of the activation of the rear window defogger is determined by various factors (coding and version of the rear window in the Climatronic Control Module -J255-, the measured outside temperature, etc.). For example, at an outside temperature of greater than + 5 °C (+ 41 °F) and a certain type of rear window, it can be switched off after only three minutes, while the maximum activation duration can be up to 20 minutes if the outside temperature is less than -20 °C (-4 °F) and there is another type of rear window installed, refer to Vehicle Diagnostic Tester in the "Guided Fault Finding " function.

The activation of the rear window defogger can also be continuously switched on (until the ignition is switched off) by pressing and holding the "rear window defogger" button on the front A/C display control head, the Climatronic Control Module -J255-. The time for which the button needs to be pressed can be set via the "Adaptation" function in the Climatronic Control Module -J255- see Vehicle Diagnostic Tester in the "Guided Fault Finding " Function and see Operating Instructions.

If the outside temperature changes during a driving period (e.g., becomes greater than 0 °C (32 °F)), the rear window defogger switches off automatically after expiration of operating times stored in the front A/C display control head, the Climatronic Control Module -J255-, refer to the Operating Instructions.

A start-stop system is available for certain engines on this vehicle. In vehicles with a start-stop system, the rear window defogger can be switched off while the stop function is active (to protect the Battery -A-). However, the setting for Rear Window Defogger -Z1- activation remains stored in the front A/C display control head, the Climatronic Control Module -J255-. After the engine is started again by the start function, the rear window defogger is switched on again, refer to Vehicle Diagnostic Tester in the "Guided Fault Finding " function.