Windshield: Description and Operation
Operation Of Heated Windshield
- Heated Windshield Control Module J505 - A - is installed in luggage compartment on left beneath Battery A (vehicle battery).
- Heated Windshield Control Module J505 - A - is actuated by Climatronic Control Module J255 (reading measured value block, display groups "045" to "047") "Guided Fault-Finding" function of Diagnostic Operation System VAS 5051.
- After starting cold engine if ambient temperature is less than + 5degrees C and Climatronic Control Module J255 is set to "Auto" mode; temperature setting on Climatronic Control Module J255 must be such that air conditioner is in heating mode and temperature measured by senders (Left Vent Temperature Sensor G150, Right Vent Temperature Sensor G151) must not be in excess of +35 degrees C; heating period is governed by ambient temperature (max. 6 minutes at -40 degrees).
- On selecting "Defrost" mode on Climatronic Control Module J255 if ambient temperature is less than + 5 degrees C; heating period is between 2 and 6 minutes depending on ambient temperature; lamp in Defrost button flashes as long as heated windshield is switched on; actuation only takes place with engine running.
- Heated Windshield Control Module J505 - A - switches on heated windshield if the following conditions are fulfilled:
- Climatronic Control Module J255 actuating Heated Windshield Control Module J505
- Voltage at Heated Windshield Control Module J505 greater than 12.70 V
- Heated Windshield Control Module J505 not overheated
- Heated Windshield Control Module J505 is actuated by Climatronic Control Module J255 by way of a signal wire. If a condition exists in Heated Windshield Control Module J505 which does not permit activation of heated windshield, this signal wire is used to inform Climatronic Control Module J255 that heated windshield is not to be activated "Guided Fault- Finding" function of Diagnostic Operation System VAS 5051.
- Resistance of metal foil in Heated front window Z2 is approx. 1.9 ohms. A voltage greater than electrical system voltage is required to attain maximum possible heat output of approx. 1000 W (watts) at windshield. The Heated Windshield Control Module J505 for Heated front window Z2 converts the electrical system voltage into a variable voltage of between 25 and 48 V depending on electrical system voltage. If voltage at Heated Windshield Control Module J505 is greater than 13.10 V, Heated front window Z2 is actuated with a voltage greater than 41 V (up to max. 48 V).
- To prevent electrical system overload, Heated Windshield Control Module J505 regulates heat output for heated windshield. With an electrical system voltage of 12.70 V this is approx. 200 W and is infinitely regulated to 1000 W at 13.10 V. Heated Windshield Control Module J505 permits an increase in power output of max. 200 W per second to guard against voltage dips in the electrical system on switching on heated windshield.
- To prevent actuation of Heated front window Z2 in the event of short circuit or open circuit in wiring, Heated Windshield Control Module J505 checks resistance of Heated front window Z2. If resistance measured is less than approx. 1.5 ohms (short circuit) or greater than approx. 3.3 ohms (open circuit or contact resistance), Heated Windshield Control Module J505 does not switch heating on or switches it off .