DIY page. Introduction to Resoldering Climate Control Unit
 

I don't know if anything is more annoying while driving than to have a malfunctioning climate control system, my personal favorite is when it is below freezing in the car and the heat is in the vents but not blowing through. The solders on the circuit board are known to have problems from time to time, this is probably the number one reason why people buy a rebuilt unit. However with this DIY rather than paying the $150 or whatever it is with the little time to take this piece apart and a $10 soldering iron you can fix it yourself for good!

Before I go on to how to fix the unit itself I'd like to elaborate on symptoms of climate control issues and the most popular problems associated with them. First is the center vents don't seem to work right, perhaps while the a/c is on the windshield starts fogging or frosting up near the bottom even though defrost isn't on. That is a bad vent pod probably caused by a bad vacuum diaphragm or a vacuum leak. The replacement diaphragms can be found many places, here is one I know of off hand. Another common problem is that the fan will only kick on if the climate control is set to defrost first with max fan speed, those are bad blower fan brushes. While you can buy a new motor for about $100 I find it much more appealing to fix it myself for $6 instead. Another common problem is that the climate control only seems to work on max or min values, quite often this can be attributed to a disintegrated foam hose which runs from the dash to the temperature sensor for the climate control. Finally, the one that we are covering here. If your blower fan turns off and on intermittently, A/C is running when it shouldn't be, and several other very odd problems then bad solders could be at fault. On my own W123 my fan would work sometimes and sometimes not, but if I hit the center console near the climate control it would sometimes turn back on.

http://207.210.95.34/~boostd/Climate/7.jpg





<meta tag> CCU, ACC, Climate control unit, Automatic climate control, Temperature, Heat, Blower, Brush, Armature, Monovalve, Defrost, Air Conditioning<end meta>

This is a good writeup. You have shown that by doing a little work yourself, a lot of money can be saved. It also shows the manufacturers are making these devices on the cheap. Not enough solder is used and breaks after a few years due to vibration.

One question though, why use flux paste? Solder comes with flux in the middle. Heat up the solder, the internal flux does the same thing.

I only had to use it a couple times, sometimes when melting the solder an oil or something would get on the pin and it'd repel the solder. I don't believe my solder has flux in the middle, also I'm primarily reusing the current solder rather than replacing the old solder. Another thing I don't think I've added to the page yet is that with a ~13W soldering iron if it is held at the end of the pin for about 15 seconds the solder which holds the pin is melted, I add another 5 seconds just to be safe. This way the boards don't have to be pulled to resolder them. :)

The problem is actually a cold solder joint here and there, not just too little solder (I'm sure they're wave soldered anyway, even back then.) Mfg speed would be the culprit I suspect. Also, rosin core solder is great for clean boards, but with old joints, some oxidation, oil, crap, etc., dousing with flux helps get a good joint despite the odds against.

Tracked down a cold solder/vibration problem that caused an intermittant failure in a radar unit on a military transport back in the early '80's (anyone else lose a few fillings on a 130?)

Everything was to mil spec, checked joints, signed off, everything, but the vibration just took its toll, despite an originally perfect joint. Things can happen even with perfect mfg (especially in a diesel, known for it's "smooth" running!)

Speaking of cold solders I actually did the same thing to my tach amp but due to the pita of removing the silicone I figured nobody else would be interested in pictures of it. It hasn't gave me any problems since. :)

How about my problem
 

When I start climbing a hill and the engine temperature starts to rise, the heater comes on.

Why would the inside temperature control care or even know what the engine temperature is, or even if its rising.:confused:

Re: Not enough solder is used and breaks after a few years due to vibration.
 

Yep, that makes sense.

Non-soldered pins
 

I now have two units that I am looking at trying resolder. I notced that they both have several pins that do not have any soder on them at all.
Is this s design thing that they should not be soldered to the board?
Should I go ahead and solder them up? None of them appear to be connected to the traces so I'm guessing that this is per spec that they should not be soldered.

Hmm, they have no solder at all on them? So this means the pin moves freely around then right? I can't imagine any of them not having any solder on them, and if they were really meant to not be soldered to anything then if they did have an output it wouldn't matter. Have a digital camera?

Compare the two boards side by side...
 

Since you are fortunate enough to have two boards, just compare the two to see if they both are missing solder in the same spots. That might confirm a manufacturing flaw.

Digi Pic
 

I'll try to get a photo of the board posted later today.

Good write-up Jeff!

Thanks Randy.

Ever come to a conclusion Fisherman?

thanks.

Mine: only works after putting on defrost, then hi.
only works at max/min values.

You gave me two great ideas on fixing these!! Thanks a ton.

Sorry, business trip...
 

I had to run down to SF for some business. I've got a couple of versions that I will shoot pics of cuz they are all a little different. If you want I can email to you also...

i have resoldered mine several times on several different cars. it's a common problem. i'm not so sure it's vibration that causes the problem though. it may be the component on the circuit board itself. some components get warm when in use. the warming and cooling will crack the solder joint. i repaired my mig welder that had the same problem. i've also repaired 2 of my t.v. sets, same thing. no vibration on the t.v.'s. just cracked joints from the heating and cooling of the individual component. with the expansion and contraction the solder gets work hardened and fails. much like bending a piece of metal back and forth until it breaks. that's my 2 cents. J.O.

Jeff aka boostnbenz, you had mentioned that the switches can be purchased. Do you mean from like Mouser or something?

I just removed the unit and have it totally disassembled. I think!?

Does the black plastic case which holds the boards come apart?

I think, from the thread, that I just solder the ones that look brown or loose. At first sight, everything is ok so I'm wondering if this will fix my CCU.(replaced my ignition switch because the CC goes off and on when it wants to.)

I'll solder what I think is bad and put it back together.
One more thing. The 'AUTO' button falls out. I don't really see anything holding it in except a small ridge on the bottom of the button?

Yes, It rotates out in relation to the switch buttons (push)

solder them all, and expecially where the two boards meet. Brown is a good clue.


The button is black, it has a white inside with two tabs, are they broken or there. You can buy just the buttons from MB

AUTO BUTTON 123.153
A1268211758

Thanks omegabenz, that helped me a lot.

Well, i put it back, or actually just connected the power to it and it seems fine. I'll see because this is what happens. First it will work and after 3-5 min. it will shut off for good.? Hopefully my solder job did the trick.

My other question is about the set of 5 lights connected together. I put the lights on and none work. I don't think that they did originally so I'm going to the Benz dealership to buy them. I have some lights with the white body only that looks like its own socket, plugged into two male electrical fittings? or ones that have that white fitting that sit in a black plastic male socket.

Either way, do they just 'pull' out or what? Do you think they will have them in stock?

Could you post a picture of your question?

Go to checker, autozone, etc, they have the bulbs. They are very small.

When resoldering these old high current connections, I find it useful to use solder wick (a braided copper material) to remove as much as the old solder as possible, or a solder sucker. Then use new solder for the connection.

SYLVANIA 2721 BULBS (I just got some at checker), you need at least 5 bulbs

Here is a picture of a bad solder joint before repair. It is the best resolution I could attain. The black ring surrounding the joint is an open crack visible with my 18X magnifying lense.

Back when I wrote that a few years ago there were several online parts places which sold just the fan speed switches for the CCU, it was the white body with everything inside of it. I don't recall if they had the temperature control knob available separately or not.

They are available here on mercedesshop as well.

I resoldered the board twice, and examined it, but I am still haveing problems. I took everything apart and cleaned it, etc.

for the w124.133 board, its working great now, but for my w123.153 I cant seem to get the climate control to work properly. Should I check anything else?

Did you resolder the pins where the side harnesses connect to?

yeah, I tried to, but that solder is very hard.

sorry to bump this thread, but it seems to be the main dicussion on this.
i just re-soldered every joint on my ccu and it performs the same task as before, just opening vents, letting heat through on defrost, but still no blower at any setting.

im not sure if i have to get inside this unit, because it explains three ccu boards but only has pictures of the unit assembeld.

what still needs to be checked on this board before i move onto other possible problem areas on the car?

my heat/ac has worked for multipe months at a time perfectly so this makes me think its something electical.

I tried resoldering several times three different push buttons, but no dice.

I bought a rebuilt one guarenteed for 3 years from programa (cost me about $225 at my wholesale discount).

I just need to send back the core ($50 core charge ontop of the $225). I was sick of messing with it.

The programma unit works very well thus far.

Austin

i went the cheaper route and got a 85 300D ccu for about $50 in a junkyard, that also did the same meaningless tasks of making a couple noises when a button is pushed. the one i repaired was the stock 81 280CE ccu. not sure if im ready to shell out that much

Disassemble the unit and check for cracked joints. There are two "wing" boards that contain the cable plug pins and are soldered to a mainboard forming a shallow 'U' shape. Then, there's another daughter board stacked with the main board -- so there's really four boards in all. I recently did mine and found that the solder joints to one of the wing boards were broken clean through.

Incidently I did a bit of root cause analysis on my CCUs solder joint failure (not that I'm necessarily qualified) and concluded that the wing board in question was soldered on at an angle, and then flexed to make the connections meet at the far end. A poor design (solder as mechanical attachment) aggravated by poor manufacturing (a flexed wing board adding additional stress). The CCU unit plastic case provides the gross mechanical strain relief for the wings, but this kind of stress didn't wasn't something it could provide the strain relief for. This might explain why these things fail if others were manufactured incorrectly like mine was.

Others have reported the switch solder joints to have failed, but mine were fine. All the cracked solder joints of interest are inside the plastic case, and there's a couple of stacked boards, so just getting to the bottom of one of the boards isn't enough.

I took copious pictures of the CCU disassembly procedure, problem, what cracked solder joints look like, etc., but I don't have time to upload them tonight (sorry), I'll try to get to them tomorrow.

http://www.peachparts.com/shopforum/diesel-discussion/185453-might-your-pet-peeve.html
Check this out....You just never know!

pictures? i like pictures ;) i just disassembled it and got to every connection except the actual external pins cause that looked like alot of work.

that is a strange find bens lover, that should be in the climate control diy section. if i figure out how to get the cover of that harness off i will take a look.

edit: i just tried looking for the wire in the picture, i didnt have it, and the covers were a real mess to get off....
actually two on that harness were not used

i didnt see any shallow u-shape joints on the inside, i fixed all joints, in and out, plus the fan speed controller and temp wheel(just figured it out after some looking). but the plug pins i left alone because they didnt seem to be under stress, burnt or cracked. but are these what your saying will fail? mine still will not work any differently so im thinking i should try those...

pics on how to disassemble the ACC unit
 

Here's the pictures I promised on how to disassemble the ACC unit...

Attachment 48572
remove the temperature unit and the cover off the fan buttons so can remove the buttons by psuhing from behind. Plastic tabs are delicate after 20 years, so careful not to break. Use penknife to slip between plastic tabs so they can be gently popped apart (ie. don't cut the plastic with it). With fan button unit cover removed, pop three fan buttons off from behind.

Attachment 48573

Attachment 48574
Pop front loose. One tab on top, two on bottom (circled in blue in previous two pictures). The front can't come off because the buttons hold it on. I couldn't figure out how to pull them off, so I did this in order to...

Attachment 48575
Reach in behind the front with a penknife so can et behind each button and pop it forward off its switch.

and on...

Attachment 48576
remove bottom cover. Three tabs (yellow circles) and then it hinges off.

Attachment 48577
With the front finally off, the fan switch unit can be removed -- squeeze tabs together gently jsut until they clear and the unit can be removed. It unplugs from the side of the ACC like the temp wheel did.

Attachment 48578
Phew. Now the cover hinges up and off from the guts. The black plastic side pieces that fit over the pins slide off over the pins. Leaving you with...

Attachment 48579
..this. Well, not exactly this, I forgot to take pictures of the inside of the w123 ACC unit when I got this far, so here's a picture of my w126 practice unit. The w123 ACC has only four relays and the circuit traces are different, but otherwise it looks the same. In this picture you can see the four circuit boards that make up the unit -- the main board on the bottom, the daughter board above it, sandwiching the button switches, and the two side wing boards.

Attachment 48580
And here's what a cracked solder joint looks like. All of these are cracked. I even slipped a piece of paper in between one to demonstrate. For me, these were visible with only the bottom removed, but others have reported that the button switch solder joints on the daugher board sometimes break, and you can't get to them without a full disassembly.

I did a detailed writeup of this over on a blog (http://w123maintenance.blogspot.com/) in case anyone is interested. Nobody reads my blog, I'm just using as a convenient place to document stuff for myself.


hope this helps :)

PatBob,

I appreciate your documentation of the process of getting inside the CCU and the re-soldering work necessary to bring some of these units back to life. I am interested in going a bit further as my CCU runs very hot in the vicinity of one of the relays. So, I would like to know what item in the hvac system each of the relays services. Once that is known maybe I can work back up to the offending item and see why it is causing such an overload. Can you or anyone here on the forum help me with this info?? Thanks in advance.

I can't help with the internal schematic.. although if you find one I'd sure like to see it. I was tempted to make my own, but didn't want to remove the daughter board to get pictures of all the jumper wires in the sandwich.

BTW, one of the common failure modes of the ACC system that I've read about is that the aux coolant pump under the hood binds and stalls. When that happens, it draws enough current that it burns traces on the ACC circuit cards. As a complete jump-to-conclusion stab-in-the-dark, you might check if that pump is the problem -- disconnect it and see if the ACC gets the same kind of hot.

thanks for the effort but its not my problem AGAIN, so i must be onto the next diagnosis... :(

Careful...
 

Those bulbs might not be the same wattage. I've melted a housing here and there using non-MB bulbs.

I'm currently trying to figure out how to put LED's in place of those little buggers. Need a 12v source to hook them up (that won't toast them also) to and I'll be set.

Hey everyone, I thought I would add something to this thread I recently "resoldered" my one climate control in my one w126..

I resoldered the joints that connect the 3 PCBs...

I also retouched the solder on the thermostat knob, dragged some down the lines that connect the knob to the pins..as well as the stuff on the fan switching side..

I also completely removed the switches PCB, checked for anything broken on it. Apparently the resistors/diode was replaced at one point in time..

I saw a couple traces that looked like they had veins running throu them or something. I decided to grab a screwdriver scrape off the material and lay down some solder in place of it.

I tell you what, I've never seen one of these control things work and change settings and whatnot this fast before. I rolled the temp wheel from cold to hot and as soon as I hit the red relays were clickin and the fan was motorin..

impressive.

Greetings:

My Little Old Lady, a 1987 300 SDL, is servicing all my needs, except the climate control.
She will start up dutifully on any Morning, however, the climate control will not start. No blower motor, no air-flow, no nothing. As the motor will warm up, HOT air will flow under the windshield, even though the blower motor is not running. You can push any of the climate control buttons, nothing will change. The HOT air will flow at the windshield, but nowhere else. You pull over the road, because you are frying, turn off the motor. Then, you start her again. LO AND BEHOLD, the climate control system is working as it was designed to work!!!

What do you think???

Of another note:
where can I buy repalcement seat cushions for the 1987 300 SDL?
OR: what alternatives are there to get the firm cushion back?
After all, she is 20-years old, 189,000 miles, IN PERFECT condition!!!
I would like to re-inforce the seat cushions.

Thank you for any and all advice,

marozsanjanos@hotmail.com

J.M.

New to this forum
 

Ok, after several hours of surfing I found this site and registered. I now know I need to replace my blower brushes, rekit the mono valve, and resolder the CCU. I understand there is a resistor in the blower circuit that could also be part of my problems. Where is it and how do you diagnose, repair, replace, or ?

There haven't been any recent posts to this thread, I hope it's still found.

Charles

The "resistor" is a metal box with wire coils; it sits on the passenger (right) side inner fender. Although anything can break, I've not heard of any actually doing so. The climate control problems that get the most play here are
(a) resoldering or replacing the pushbutton control unit,
(b) rebuilding or replacing the monovalve,
(c) rebuilding or replacing the auxiliary water pump (remember to add a fuse),
(d) replacing the brushes in the fan motor or replacing the entire motor (my brushes had worn into the commutator so much that I had to replace the motor),
(e) replacing the disintegrated foam tube that connects the interior temp sensor to the blower intake, and
(f) rebuilding, replacing, or working around failed vacuum pods (that move the doors to direct air here and there).

This does not count repairs to the refrigeration system, which can be a whole set of problems by itself, nor does it cover bad thermostats, clogged radiators and heater cores, and other parts of the engine coolant plumbing.

Mercedes designed the climate control system to default to "hot air to the windshield" as a safety measure, so you could always get your windshield clear of moisture, ice, etc. If you have a problem where that occurs sometimes but not always, the electronics are probably getting flakey. Someone here probably has had that exact problem and can tell you what to do.

Jeremy

Thanks
 

I hope I'm doing this post right. In my surfing I found instructions on rebuilding seat cushions using pool noodles - I think on this forum under another topic.

Also, my thanks for a run down on ccu issues. Mine seems to fit the solder cracks discription in that some times it doesn't work at all and other times it works great.

Charles

I'm one of the "lucky" few who've had the blower resistor fail. One of the coils just burned-up. I ohm'd-out about everything imaginable, installed two different CCU's that I'd repaired and that worked perfectly testing them (at least till this point) and checked everything you could imagine. I would never have imagined the blower resistor going out. It did though, so ever since then, I pull them at the junkyards and have a dozen or so in parts stock in the basement....

OK, so I'm obsessive about not having to pay retain for something if it breaks....

dude! that's the car making sure it doesn't overheat! It's alive!

i found out this weekend that ACC units are not universal between 123 and 126. bummer.

my unit works okay, i.e. does not need resoldering, but sombody fat fingered the buttons and broke the spring keepers off most of them. as far as i can tell, i need to completely unsolder them from the boards and replace the whole pushbutton thingy. Anyone got a trick to replace the button posts without removing the whole switch body?

I soldered up the CCU and cleaned out the fan switch, but I still have no fan control. The rest of the CCU seems to work fine. I also cleaned the contacts on the sensor just above the thermostat housing with no joy. What is next, the fan its self?