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Heated Windshield






Heated Windshield

=> [ Heated Windshield Function ]

=> [ Windshield Heater, Deactivating ]

Heated Windshield Function

• The heated windshield control module (J505) - B - is actuated by the Climatronic control module (J255) A/C control head (read measured value block, display group "015").





- After every cold start of the engine if the outside temperature is less than + 5°C and the "auto" or "defrost" operating mode is set on the Climatronic control module (J255) A/C control head. The temperature must be set on the Climatronic control module (J255) A/C control head so that the A/C system is in the heating mode and the temperature measured by sensors left vent temperature sensor (G150), tight vent temperature sensor (G151), left footwell vent temperature sensor (G261) and tight footwell vent temperature sensor (G262) must not exceed + 35°C. Depending on the outside temperature, the heating period is a maximum of 6 minutes (at -40°).

- When selecting the "defrost" operating mode on the Climatronic control module (J255) A/C control head if the outside temperature is less than + 5°C. Depending on the exterior temperature, the heating period is between 2 and 6 minutes. As long as the heated windshield is activated, the activation indicator light in the the Defrost button flashes (only when the heated windshield was not already activated by the Climatronic control module (J255) A/C control head when the Defrost button is pressed). Activation is performed only when the engine is running and the above described activation conditions are met.

• The heated windshield control module (J505) - B - activates the heated windshield if the following basic conditions are met.

- The Climatronic control module (J255) A/C control head actuates the heated windshield control module (J505).

- Voltage at Heated Windshield Control Module ( J505) is greater than 12.70 V.

- Heated Windshield Control Module (J505) is not overheated

• The heated windshield control module (J505) connects approx. battery voltage to the Climatronic control module (J255) A/C control head. This indicates to the Climatronic control module (J255) A/C control head that the heated windshield control module (J505) is ready to activate the heated windshield. If this voltage is halved by the Climatronic control module (J255) A/C control head (approx. 5 to 8 V), the heated windshield control module ( J505) activates heating.

• The electrical resistance of the metal foil in the heated windshield (Z2) is approximately 1.9 ohms. A voltage greater than the electrical system voltage is needed in order to reach the maximum possible heat output of approximately 1000 W (Watt) on the front window. The heated windshield control module (J505) converts the vehicle electrical system voltage into a variable voltage of between 25 and 48 V, depending on vehicle electrical system voltage. If a voltage at the heated windshield control module (J505) is greater than 13.10 V, the heated windshield (Z2) is actuated with a voltage greater than 41 V (up to max. 48 V). In the case of poor heating output of the heated windshield (Z2), check the voltage at the two connection points of the two wires on the windshield. Activate the heated windshield (Z2) via the " output diagnostic test mode" function with the engine running and a fully charged battery (the vehicle electrical system voltage must be greater than 13.1 V).

• To prevent electrical system overload, Heated Windshield Control Module (J505) regulates heating output of heated windshield. At vehicle voltage of 12.70 V, output is approximately 200 W and is gradually increased up to 1000 W at 13.10 volt. To prevent vehicle electrical system from collapsing when heated windshield is switched on, Heated Windshield Control Module (J505) allows for an output increase of 200 W per second.

• To prevent activation of the heated windshield ( Z2) in the event of short circuit or wire break, the heated windshield control module (J505) checks the resistance of the heated windshield (Z2). If the measured resistance is less than approx. 1.5 ohms (short circuit) or greater than approx. 3.3 ohms (open circuit or contact resistance), the heated windshield control module (J505) does not activate or deactivate heating. Check the wire connection between the heated windshield control module (J505) and the heated windshield (Z2) for contact resistance or short circuit. The measured resistance between the two wire connections of the heated windshield control module (J505) (to the heated windshield (Z2)) must be less than 2.5 ohms and greater than 1.4 ohms

Windshield Heater, Deactivating

• The heated windshield control module (J505) is installed in the plenum chamber under the battery (A).

• If a crack forms in the windshield due to an outside influence (e.g. stone impact), switch off the windshield heater so that the crack does not grow.

• So that the function of the A/C system is not limited, disable activation of the heated windshield control module (J505) until the damaged heated windshield (Z2) is replaced. To do this, disconnect connector - A - from the heated windshield control module (J505)- B -.





• Depending on the version of the heated windshield control module (J505), the connector (connector - A -) is not located directly on the heated windshield control module (J505) but in the wire connection in the travel direction to the right of the battery (A). Connector - B - to the heated windshield is located at the same location.





• The Climatronic control module (J255) A/C control head does not activate the heated windshield control module (J505) in the "Econ" operating mode.
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