Thread: HEVAC Backlight - Tips from experience

That book symbol showed up again. Stripped the panels and then the dashboard AGAIN so I could have a good look see. Pulled the motors, checked the flaps for binds and then reassembled. Hooked up the Nanocom and observed. However the HEVAC LCD was now blank. All the other lights were working. Thinking I may have shorted something etc. I jumped on internet and found lots of horror stories about this display. In a moment of 'brain fade' I stripped the HEVAC to check the ribbon connector. All seemed OK so reassembled and switched on again. Still no LCD. First penny dropped - grabbed my miniature LED snake light and backlit the screen - and its all there working. Checked voltage to back light bulb - zip. Checked grounds - OK. Read all the wiring diagrams and wrote down all the points to check on the way back to the BECM. On the way I noticed on Circuit Diagram k4 DIA 4 right at the bottom, the Instrument cluster was shown - why the heck is an instrument cluster showing here in the HEVAC. Second penny drops - the voltage to the HEVAC back light bulb comes from CO233 - and I had stripped the instrument cluster out whilst testing. Plugged it back in and all of a sudden there is light!

Two tips - before you go disassembling the HEVAC for a display problem - back light the screen with a small torch and see if the display is working.
You need that 'instrument panel' in the circuit otherwise there is no power to that bulb. Whoever designed this?????
Hope this helps someone in the future.
Oh = no book symbol now. A bind in the LH Blend.
Cheers

I'm surmising the instrument cluster is there because the HEVAC display is tied to the dimmer on the indicator stalk..?
Thanks for the tips. I'm also getting the book symbol...but only on hot days. When the ambient temp stays below 20 degC the book symbol is absent...I'm guessing it's a binding flap valve due to heat distortion of the heater box. Suspect I'l have to remove the dash and attack heater box... and perhaps do the Audi heater core job as well while it's all disassembled....