Pre Facelift D2 Retro Fitted Heated Front Windscreen

[ikillcopiers]

Hi all,

On the advice of Notorious, who's really helpful, I'm posting here in the forums on this query.

I have a Pre Facelift Audi S8 D2, in which I am about to fit the front heated windscreen from the Facelift model.

We have ordered the screen from Audi, and I have the heater module/ecu/amplfier from A8Parts.

Notorious had a lot of useful information on running the wires up to the screen, and how he connected in to his car.

However, one little niggle I have is how to activate the heater module.

There are two wires that connect in to the HVAC in order to activate it, before I start experimenting does anyone have any experience as to how these are used to activate the heater module?
Is it just a case of a simple switch to ground it out, or does it need 12v, or does it use a signal from the HVAC?

I was hoping to wire a switch in my dash similar to my rear heated window switch, in order to activate it manually.

Does anyone have any experience with such a setup, or the operation of the heater module?

Thanks!

[David's8]

It comes on either manually by selecting the appropriate screen heating button (which you wont have I guess) on the CC module or automatically when the outside temp is <5degC and the CC is in Auto mode. But how the switching is achieved I am not sure.

[notorious]

Hi David, on my FL it never comes on automatically. Only when I press the windscreen button and when outside temp is below +5C.
Perhaps I forgotten to code something in the HVAC module after I retrofitted the system into my car.
Or maybe because I keep the car in heated garage, so there was no situation for HVAC to switch it on automatically.

[notorious]

Information from ELSA for facelift cars:

Functional description of heated windscreen
* The heated windscreen control unit -J505 is actuated by the operating and display unit -E87 (=>Read measured value block, Display group 019)
* After every engine cold-start if the ambient temperature is less than + 5°C and "Auto" mode is set on the operating and display unit -E87. The temperature at the -E87 must be set so that the air conditioner is in heating mode, and neither of the two vent temperature senders (-G150, -G151) should measure more than + 35°C. The heating period lasts up to 4 minutes, depending on the ambient temperature.
* When "Defrost" mode is selected on the -E87 if the ambient temperature is less than + 5° C. The heating period lasts between 2 and 4 minutes, depending on the ambient temperature. The indicator lamp in the "Defrost" button flashes while the heated windscreen is switched on. The heated windscreen is only actuated when the engine is running.

The heated windscreen control unit -J505 -B- switches on the windscreen heating if the following conditions are met.
* The operating and display unit -E87 activates the -J505.
* The voltage at the control unit -J505 is greater than 12.70 V.
* The control unit -J505 is not overheated.

The electrical resistance of the metal foil in the heated windscreen -Z2 is approx. 2 ohms. To enable the heated windscreen to attain the maximum possible heating power of approx. 1000 W (Watts), a voltage greater than the vehicle electrical system voltage is required. The heated windscreen control unit -J505 converts the vehicle voltage into a variable voltage which, depending on the vehicle voltage, is between 25 and 48 V.

To prevent the vehicle electrical system from being overloaded, the -J505 regulates the heating power of the heated windscreen. At a vehicle voltage of 12.70 V the heating power is approx. 200 W, and it is regulated steplessly up to 1000 W at 13.10 V. To prevent the vehicle voltage from collapsing when the heated windscreen is switched on, the -J505 permits the specified power output to rise by a maximum of 200 W per second.

During activation of the heated windscreen the voltage at the fresh air blower -V2 is limited by the operating and display unit -E87 (to approx. 4V in "Auto" mode and to approx. 7V in "Defrost" mode).

Disabling heated windscreen
* If a crack develops in the windscreen as a result of some external impact such as a stone chip, the heated windscreen is disabled to prevent the crack from growing.
* The operating and display unit -E87 does not activate the heated windscreen control unit -J505 in "Econ" mode.
* So as not to restrict the functioning of the air conditioner, the heated windscreen control unit -J505 must be disabled until a damaged heated windscreen -Z2 is replaced. To do so, unplug connector -A- from the control unit -B-.

[notorious]

On FL cars there is only one wire (yellow/black colour wire) that connects the heated windscreen with HVAC module (the one that you disconnect to disable heated windscreen functionality from above ELSA article).

[mattylondon]

Originally Posted by notorious

I didn't find information in ELSA about communication 'protocol' on that wire between HVAC module and the heater module in the boot.

It's a bi-directional wire with a wave form of the heating demand. Be great to get an oscilloscope on there just out of interest.

[notorious]

Cheers Matty!



Continued.
Explanation from ELSA about Display Group 19, Display zone 4, which sheds some light on specifics of the protocol of the yellow/black wire that connects E87 (connector D, contact 11) with J505.



* "0" or "00" is displayed if the vehicle does not have a heated windscreen or control unit -J505.
* The heated windscreen control unit -J505 switches approx. battery voltage to the output to the -E87 as long as the voltage at the -J505 is greater than 12.70 V and the control unit is not too hot.
* If the windscreen heating is to be switched on, the operating and display unit -E87 actuates a transistor which reduces the voltage at connector D, contact 11 by 50%. The control unit -J505 switches on the heated windscreen.
* If the voltage (vehicle voltage at -J505) falls below 12.70 V while the windscreen is being heated or if the control unit -J505 becomes too hot, a switch in the -J505 opens and the voltage at the output to the -E87 falls below 5V. At the same time the heated windscreen is switched off by the -J505.

That hopefully is aligned with Matty's content.

There is a lot of further reading if you google for "E87 J505"

[notorious]

Interesting manual that includes info about J505

[mattylondon]

Originally Posted by notorious

Interesting manual that includes info about J505

I only had the German version
Superb

[ikillcopiers]

Hi All,

Thanks for the info, Sean (my electrical guru) and I have been pouring over it, and whilst the information is quite useful, we're still not 100%.

It suggests that the signal is bidirectional.

We need to confirm exactly what kind of signal goes through the line, IE is it a DC signal of sorts, as in signal to ground to come on, OR, is it a data transfer, which is suggested by the byte bidirectional (otherwise known as a linline).

The ultimate would be if someone could hook a scope up and see what happens in the wire.

We're going to try grounding the wire on the unit outside the car in the hope that it will "trick" it in to coming on, however we're suspiscious that this may not be the correct signal.

Any help appreciated, thanks in advance!