Climate control Solder repair advice needed. - PeachParts Mercedes-Benz Forum

Merkey · #1 07-25-2006, 10:05 PM

Hi People,
My sons 1988 300TE is showing all the signs of needing a Climate control resolder.

Sometimes blows hot, out of defrost and side vents when you need cold.
High fan speed selected and functioning then suddenly nothing.
Low speed then nothing
Switching to defrost will sometimes restore it to working, othertimes a slap in the side of the console or facia will get it going again.

So, it looks like dry solder joints.
I have searched a few times and have a basic idea, but just wanted to ask based on the above which joints to solder that may fix the problems?

Merkey · #2 07-28-2006, 11:37 PM

>>>>>>>>>>>>Bump<<<<<<<<<<<<<

Just hope that someone can help before I pull it out and do it blind!

sixto · #3 07-29-2006, 12:24 AM

That vintage of PBU is very different from the units with external temp controller. There are a few tricks to getting the cover panel off. Then more tricks to getting the card to come off the main board. Having done all that I took mine to a friend who had professionals at work 'reflow' the solder joints. Didn't help one bit. What worked was a rebuilt unit for less than $200.

Sixto

#4 07-29-2006, 12:31 AM

Try this one, it has the pointers you are after,

anybody ever resoldered AC Type II Control Unit?

I had success with fuel pump relay also

Merkey · #5 07-29-2006, 06:00 PM

Thanks for your input Guys...
Well, we took the Climate Control Board out... 2 Screws, and remove the wood facia, then 2 more screws, pull off the electrical connectors and we were on the bench and ready!
We had problems pulling the covers off and broke one of the fan control buttons...
But here is what we saw....
Look at the burned connections on the back of the circuit board, outlined in red... a clue or what??

Here is the flip side of the board with the componant that was on that burned connections, outlined in red too. The glue that holds the part in place was also showing signs of overheating. I could feel the unit was loose!

We carefully heated the solder on those 3 points and also I did the points on the fan speed switch....we put it back in and it works just fine now... well so far I guess would be better to say!
We are happy!
Thanks to everyone!

mpolli · #6 07-29-2006, 07:40 PM

It is always a good idea to remove the old solder and use new solder. You can remove the old solder with "solder wick" or a "soldapullt". The old solder gets kind of crusty. You want a shiny joint when you are finished.

Mike

Merkey · #7 07-30-2006, 06:57 PM

That sounds like a lot of work!
Never having done ANYTHING like this before, I was pleased to have got the job done and the ACC is now working!

Does anyone know or have a good method for getting the buttons off without breaking them?
Does anyone have a supply of these ... Fast Fan button in particular?

JohnnyLuv · #8 08-03-2006, 06:24 PM

Did you find out how to not break the buttons, get them off easier?

Merkey · #9 08-03-2006, 11:48 PM

Nope... still hoping someone will reply!

Kestas · #10 08-04-2006, 12:03 PM

There should be nothing wrong with old solder unless it is oxidized or dirty. The issue is to get the solder to wet both adjoining surfaces. Repair could be as simple as dabbing some flux onto the area and reflowing the solder. There's a tounge-in-cheek saying that "a clean joint is considered already half-welded". Heck, it may even work without the flux. The other caveat is to not overheat the electronic components any more than is necessary.

mpolli · #11 08-04-2006, 01:31 PM

Correct. However, old solder by definition will be oxidized and dirty. The act of reworking it causes that result along with whatever caused it to fail in the first place. If it already failed once why re use it? You can get away with re-using the old existing solder just like you can get away with a lot of things. But it is not correct way to do the work. I am speaking from professional experience however so you might not demand that level of quality in your work since you can just fix it again if it fails again.

Mike

rickpark · #12 08-04-2006, 02:13 PM

Sounds like it is working OK but if I saw that kind of discoloration, I'd be worried that the semiconductor was subjected to abnormal current levels and likely to fail after you put in the hard work to pull, diagnose/resolder and replace.

At least if it happens again, you have a likely suspect for replacement.

FYI, here is a datasheet of this part which is a 5v voltage regulator.

riethoven · #13 08-04-2006, 02:59 PM

Quote:

Originally Posted by Kestas

There should be nothing wrong with old solder unless it is oxidized or dirty. The issue is to get the solder to wet both adjoining surfaces. Repair could be as simple as dabbing some flux onto the area and reflowing the solder. There's a tounge-in-cheek saying that "a clean joint is considered already half-welded". Heck, it may even work without the flux. The other caveat is to not overheat the electronic components any more than is necessary.

I actually had an area on the board that had a break in the copper foil and couldn't get the solder to bridge the break. I got three strands of fine copper wire and soldered them to span the gap in the copper foil. I checked for conductivity and it is there. My ACC is still not working, but I recieved my W123 maintanence discs today so I am ready to get this thing working.

Rick76 · #14 08-04-2006, 07:59 PM

Best way to remove the buttons on most Mercedes pushbutton assemblies (the ones made by MK) is to remove the bottom cover and press them off from the rear. Make sure you give even pressure as you can break the switch shaft if you are not careful. I usually use two small screwdrivers or a pair of thin long nose pliers.
Your unit is the Bosch however. By uncliping the front cover (4 places) you can apply pressure to the cover to pop the buttons off.
Replacement buttons are available from the dealer parts department, however there are lots of scrap units around. Know any Mercedes mechanics? They usually have a few under their workbench.

Merkey · #15 09-07-2006, 09:37 AM

Looks like it has failed again.
Its acting up pretty much the same.
Anyone have a supplier for the L4705, so we can get in there and replace it?
What is the glue stuff that surrounds the base of the componant and what should we use to replace it?