I've got the climate control unit pulled from my '86 560SEL, following this DIY:
Fixing that Damn Climate Control!
http://207.210.95.34/~boostd/Climate/

I am unsure what needs to be soldered.
Is it where the three pieces of white filament connect to the three circuit boards? Anything else to check while I'm in there?
Thanks for any help,
Mark

You need to resolder any dry joints. A dry joint is usually obvious because the original solder joint will be of poor quality.

Look for any joints that are lifting from the PCB. Also look for any joints that are spherical, as opposed to conical (which is the shape they should be).

Do not heat the board up too much, or the track will start lifting and then you'll be into hard wiring components which is messy.

As Parrot said, don't heat it up too much. The worst thing you can do is to use a high power soldering iron. A 25 Watt will do fine.

Good luck,

Are there any particularly likely trouble spots I should pay especial attention to?

The basic problem is that when the circuit board was made they used less than the required amount of flux at the solder joints and then used a process called "wave soldering" to apply the solder (the circuit boards float across a pool of liquid solder like corn flakes atop milk on a cereal bowl.

This flux (the goo that makes the solder flow into the joint) appears white on the circuit board at the solder joint, a tell tale indicator is small cracks across the surface of the solder joint. Use a magnifier to enlarge your close view and you will see them. This is the major cause of relay and module failure in 90% of the relays and control modules on the market. (Hella, Bosch, etc ALL are "Hecho in Mexico" or China where QA is a theme ride but not reality).

Use the cheapest Radio Shack iron and don;t add any solder, just touch the tip to the bad joint for a second until the surface gets shiny or flows and STOP and let it cool and set and that should do it.

Believe me, MB ain;t the worst- 99% of all the "no start" conditions on Volvo, Audi and VW are caused by relays or control modules where the circuit board was wave soldered.

I will add 2 points to the above info:

1) Wave soldering is not inherently bad. There are other variables involved. The main problem is using a single sided (copper only on one side) circuit board vs. 2 sided. The 2 sided boards have "plated through" holes. These "suck up" solder and make a better joint. Single sided boards just have solder on the one surface of the board. This especially a problem for any parts that get hot. Cracks develop for the same reason that cracks develop in asphalt. The solder heats up and expands, but when it cools it is not flexible. After many cycles a circular crack will develop around the pin. This is one reason why surface-mount is so much more reliable than through-hole technology.

2) I strongly disagree with the advice to not add more solder. Ideally you would remove the old solder and add new with flux (flux core solder). As a second best option I would add some flux core solder. Old solder does not solder well. It becomes oxidized.

Mike

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

I agree with Mike. You must add new solder to the joints.

Model year 86 was the first year of the North American W126 to have electronics in the pushbutton assembly. Before that it just had switches and relays.

On the 86, resolder the joints of the pushbutton switches and temperature control potentiometer. Also look for cracks on large components such as the regulator IC, driver transistors and driver IC's.
Also there are 2 capacitors that sometimes leak. They are 33uF/16V (one on each board).
Look for signs of overheating of components. A seized aux. water pump or shorted monovalve can damage it's driver transistor in the push button module.

As a side note, if the numbers on the temperature wheel are not so nice (they separate or peel off), they are available as a replacement part for a few dollars.

Does the entire unit need to be removed to replace the tape? If so, does the potentiometer need to be disassembled, or is it easy to replace the tape once the pot is off the unit?

THANKS RICK! As soon as this #@$%^& winter weather clears, I'll replace the tape.

__________________
1986 560SL
2002 Toyota Camry
1993 Lexus

The temperature wheel must be removed from the unit to replace the number strip. Peel off the old strip and clean the wheel well - isopropyl alcohol works (not rubbing alcohol).
Part number for Celsius is 124 821 29 67 and Fahrenheit 124 821 34 67.
This strip will fit W123 (from MY 81), W124, W126, W107 (from MY 82) and W201.

If you are messing around with electronics and solder, do NOT use plumbing (acid) flux - EVER! You will end up with a nice looking solder joint that will eventually become worthless once the acid flux eats up the copper traces. Electronics solder has its own flux, which is usually a liquid or is embedded in the solder core.

Also, if you are going to add more solder be careful and do not add too much. "The bigger the blob, the better the job" doesn't apply here. If the joint is grainy and a big blob, remove the old solder first with a desoldering pump or with solder wick. Then try again with fresh solder.

Here's a nice link to a soldering howto:

http://www.mediacollege.com/misc/solder/

__________________
1984 300TD

I resoldered all of the points pertaining to the pushbutton fan controls, on its proprietary board, and where its filament connects to the mother board, and the fan still only works on low speed, regardless of the setting. Any hints what's next?

Usually solder cracks on that particular climate control module are limited to the largest of the 3 circuit boards.
Never seen them on the small fan switch board.

Thou scribeth: "I resoldered all of the points pertaining to the pushbutton fan controls, on its proprietary board, and where its filament connects to the mother board, and the fan still only works on low speed, regardless of the setting. Any hints what's next?"

Resistor pack...?

For those just joining, I've got an 86 560SEL with a CCU in need of some help. That's for sure, because I was able to try a good one. I swapped in a good CCU which by the way has a completely different looking board (this one's from an 88 300E) and the blower works on high and low, but air is not cold, though the AC line running along the drivers side of engine bay is cold. This CCU does run cold air in the 88 300E. So something on my CCU board that has to do with offering high-speed fan is kaput.

1. What on the main board controls the fan?

2. What else may be wrong with this car that is keeping cold air from being offered from the vents?

Gurus, shotgun solutionists, hacks,
I offer myself (along with my problems)
For your perusal,
Thanks,
Mark