That it went completely dark makes me think it is a fuse. There are other fuses hiding around on our car...IDK if hvac control has one built into the back of it, but that's possible...and then there are fuses in the e-box (under hood) and behind fuse panel.
Check Bentley or spaghettidecoder.org and see if you can find a blown fuse and/or maybe a burned up wire/connection.
If you have any aftermarket electronics installed at all, I'd begin by looking at them.
First time I recall reading about the control unit going dark, so hope you figure it out soon.
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Mangofy your E46!