HVAC controls froze

The weirdest thing happened the other night when I was driving home on the interstate. I reached down to turn on the defrost because my windows were fogging up and when I pressed the button it wouldn't turn on. I tried changing the temperature settings and the fan speed and they didn't work either. The HVAC display was frozen and none of the controls worked. I had to pull off to the side of the road because I couldn't see squat out of my foggy windows and even when I turned off the car and took the key out of the ignition, the HVAC system stayed on and kept blowing. I ended up having to disconnect the battery to get the darn thing to turn off. Anyone else experience something like this? I guess I should have expected sooner or later I'd experience some sort of electrical bug...german cars don't exactly have the best reputation for reliability in that area.

There is this thing - Blower Motor Resistor aka Final Stage Unit. When it goes bad the usual symptoms are erratic fan behaviour or even HVAC controls failure.

I'm not 100% sure that's your case but it looks like it might be it. Research it and see if someone else had the similar symptoms due to FSU. The part is not expensive and it's like 30 minutes diy.

Good Luck!

It does sound a lot like the blower resistor - I've already replaced mine twice. The first time it went the blower wouldn't turn on, the second time the blower was stuck on and I had to take out the fuse to turn it off. Relatively easy fix on my car - had to pull the glove box out and feel around behind there. If you do a search you'll find a bunch more information on it. Good luck.

Thanks for the help guys. I searched through the site and found quite a few threads discussing the same problem just like you said. Sounds like the resistor might be a little tricky to get at but it's a relief to hear it's actually a relatively common issue with a straightforward DIY fix rather than something more serious.

The same thing has happened to me twice in the last 5 years.

Pulling the fuse is faster than disconnecting the battery.

It's not the final stage resistor.