I couldn't find a detailed guide to this, so I made one just in case.

The W123 HVAC is pretty funny, because half of it relies on vacuum actuators and stuff (if your center vents don't work, that's why), and the other half relies on PCBs soldered at 90° to each other and then subjected to (usually) diesel vibration for 30 years. Failure of the latter can cause the HVAC not to come on, to come on sporadically, or to come on full-heat or -cool. So re-soldering is a good way to go. Let's do that...



The first step is to pry the wood off. It's held on by four pegs, and if you side a flathead driver behind it, it'll just pop right off. Then you're left with this.

Removing the unit as a whole is pretty simple. One removes the upper-left and -right screws, puts a flathead driver into one of the flat apertures inboards from either now-vacant screwhole, and rotates the unit down, pivoting on tabs that sit above the radio. That gives one this.

Wiggle the lights free (now is a great time to change them), and only two large connectors on either side remain. Removal is straight-forward.

Once the thing is out, remove the faceplate by undoing the remaining three Philips-head screwdrivers. That leaves the unit itself. The next step is to remove the temperature wheel—pretty straight-forwards. Just compress the clip on the top with needle-nose pliers and pull the wheel module off. Careful with the clip.

Pop. Next, we'll take the cover off the fan-speed switch. This is pretty straight-forwards too. There's three clips, one on each side. Take a flathead to them. Keep track of the little pivot inside the fan-speed box. It goes long side-up.

The next step is to remove the bezel around the buttons. One clip on the top, two on the bottom, and it pops free. But it won't come off. Before that, one has to push the buttons out from behind the bezel, now that it's loose. I find that inserting a big flathead wrapped with a layer of electrical tape, then rotating it 90°, works well. The "AUTOM." button is a bit tough. But the buttons pop off, and then the bezel comes free.

The next step is simple. Remove the light pipe.

Now we're getting somewhere. Next, we'll look on the back of the unit, and find three big clips holding on the piece with the part number. Take the flathead to them, and then pivot the piece off.

Now turn the unit over. Repeat the procedure to remove the temperature wheel to get the fan speed module off. Careful of the clip, once more.

Now we have the main unit alone. Turn it so that you're looking at the PCB, and, using the tape-wrapped flathead, pivot it open from the back of the unit.

Remove it entirely. Now repair is just a simple matter of re-flowing all the solder connections that join the 90° board's traces to the main board, on each side, and repeating this procedure in reverse. I might also suggest using something to clean the pins on the side, and using dielectric grease when you're plugging them back in. The latter two pictures in this series show dirty and cleaned pins respectively, for reference.

Note: This is a JM Classique™ post. Photobucket are a commercially-operated research seaplane of some kind, where was I going with this? I wish my job was flying seaplanes, and broke image links from ten years ago, removing the images from old forum posts. Since I’m going through each old post and re-hosting the image on this server, I figured I might as well shove the post here, too. JM Classique™: Your Trusted Brand of Yestercrap.

 

Once upon a time there was a company called SAAB, and they lost their monies, or misplaced them, or at any rate they didn't have any any more. This was a bad thing for SAAB, and they stopped making cars, which was what they did and I just didn't mention it because the context should have made that clear. A million billion and seven-eighths miles a way, a young tycoon named Vaddington L. Bear Esq. woke up and realized that he had lots of monies! This made him very happy, and he decided to go absorb SAAB (whose troubles he had heard of using a wireless radio) into his moobclave and use his monies to help them.



When he got there, SAAB was all messed-up. The thingy had fallen off whatever and they had no beaver statues. Vaddington L. Bear Esq. tried yelling on-the-spot guidance at them, but that didn’t help. He decided that he would help SAAB by using his monies, despite the counter-revolutionary thought such an action would entail.



Unfortunately, Vaddington discovered that SAAB’s creditors (which is a thing imported from the decadent West, whereby foul goblins disrupt your self-reliance and have sex with your family) wouldn’t give SAAB to him! They wanted more monies—and they knew somebody with almost as much monies as Vaddington had...



Vaddington L. Bear disagreed.



After the creditors were dead, Vaddington marched right into the factory. “I have monies,” he announced, “Western imperialist monies!” The trolls inside jumped for joy, because now they could do the things they did before they ran out of their own monies—frolic and build cars and besmirch Volvo and race swans. They adored Vaddington, even though he ate a couple of them, and they crowned him the new Most-Equal of SAAB. He reigned over the People’s SAAB Construction and Marketing Combine no. 34 for a thousand years, with an iron fist and a loving claw, and the trolls lived happily ever after.