HVAC Screen backlight

[SquattyD]

After a long search I still can't find any answer. Ever since I got the car, the HVAC Screen has never lit up. I have removed the unit and pulled it apart looking for some kind of led or something. The button lights all work and the unit works, but I can't read the screen in low light and hardly read it in bright light.

So the question I have is, is there a bulb or does the unit need to be replaced?

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[Qsilver7]

Have you opened the IHKA up to where you can test/check the display? Perhaps the display has failed or a solder joint or connection to the display has failed. It's obvious that work has been done "around" the IHKA based on the image you posted...there's a modifcation to the cup holder. So is this the original IHKA? Or has the original IHKA been replaced?

You have no model/model year info...so we don't know if the IHKA has been upgraded from from the one with REST to one with the MAX button.

Here's a video that shows opening the e39's IHKA: https://youtu.be/B1C0flm-31g

Below is a pic of the e36 IHKA...the e39's would be similar:

[SquattyD]

My apologies, I thought I had updated my info so my car was up with my location. I was wrong on that one. I also didn't realize how crappy the picture was. It is a 2003 530i, it has the factory unit (so yes the max button was factory and what I have). I pulled it apart just like the pictures you posted expecting to find a small led soldered to the board behind the screen. The screen itself works. It shows the temps, fan speed and everything; it just doesn't light up. All of the buttons light up when the lights are turned on, the indicator lights in the buttons also work fine. Circuit board looks good as well, no corrosion or burned marks anywhere on any connection. I just didn't see where the screen gets the light from either.

[Qsilver7]

Hmmm...thanks for the additional info.

The IHKA has a small ambient light sensor that is supposed to help with adjusting the brightness of the display. There should be a little white square in the right air vent/grid on the front. Perhaps that light sensor or the traces to it on the circuit board has been damaged. If not that, then the dimmer switch (on the dash) also affects the IHKA's display.

[SquattyD]

I may pull it again an poke around to see. The dimmer works for everything else so I doubt that is it. I was also wondering if there is a wire in the harness for the display light or if it just turns on with power to the system. I assume it should light up like the radio when the lights are off too.

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