How to repair w123 v2 climate buttons

[chrisgt]

I searched the internet and didn't find anything useful on v2 climate control buttons that wouldn't stay in. So I took the silly thing apart and figured out how to fix it. This is what I did.
First you need to remove the hvac unit, this is a pretty good guide.
Then you have to take it apart, I followed this guide.
While you're in there, reflow the solder joints, even if they aren't cracked. Mine didn't look cracked, but when tested with a solvent I could see tiny cracks forming.

From here on out I was on my own with this repair. I should have taken more pictures, but I didn't...
This is the top of the the circuit boards, that little board on the top of the buttons has to be removed.
It's a pain, you have to suck all the solder out of every pin of every button to remove it.


Next you can unfold the little metal tabs that hold the buttons in. I don't have a great picture, but you can see the tabs here with a button removed. It's pretty obvious once it's all apart.

(we'll come back to this picture later...)


Two of the buttons have a springy thing folded under those tabs, I got zero pictures of these. THESE MUST BE REINSTALLED CORRECTLY. So take note of how they came out, they tension the rod thingy that make the buttons work.

Once you have all the tabs folded up, springs removed, flip the unit over and desolder all the button pins. This will take you a while. It's probably also a good time to note that circuit boards from 30 years ago are VERY DELICATE. If you use too much heat, too much pressure, too much scrubbing motion you WILL lift pads off the board and ruin traces. Be extremely careful and try to avoid using solder wick if at all possible. Use the sucker type solder removal tools.

This picture does a good job at showing what goes wrong, look at the black tabs sticking up. Those go into notches in the buttons, when you press a button that tab locks the button in because the aforementioned springs pull the whole rod assembly into the button. When another button is pressed the rod is slid over, releases the current button and locks the newly pressed button in place. Obviously it does not work with the corner of the tab missing.

The left tab is healthy, the right tab has a bite out of it. Make sure to find those pieces of broken plastic and get them out of the buttons!
Also note: the metal channel should only be installed one way, the pic shows the little indents on one side, but not the other.



Here's another view of the rod removed.


One would expect that since only two of the tabs were broken all but two buttons would stay in, however none of them worked. This is because the broken pieces were in there jamming things up, which is why it's important to remove them.

I fixed the tabs by cutting the offending ones in half then supergluing on a small piece of plastic. It really doesn't matter what you used, I broke a piece of ribbing off a milk crate. Glue on a piece that's too big because you can always file it down to the correct size after the glue dries.

After that put everything back together the way it came apart and your hvac buttons will work again!

Now go pet your cat, he's mad you've spent 3 hours working on your car not petting him.


I really hate the way the auto climate control works, even now that it works properly. The center vents only occasionally blow air, according to the manual this is normal operation... If I find another unit at a junkyard or some such I wanna reverse engineer the system and build my own digital control module. That way I could program it to work however I want. Or just program it to work...