DIY page. Introduction to Resoldering Climate Control Unit - PeachParts Mercedes-Benz Forum

BoostnBenz · #1 02-16-2004, 10:56 PM

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.

CCU, ACC, Climate control unit, Automatic climate control, Temperature, Heat, Blower, Brush, Armature, Monovalve, Defrost, Air Conditioning

wbain5280 · #2 02-17-2004, 02:54 AM

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.

BoostnBenz · #3 02-17-2004, 10:06 AM

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.

TomJ · #4 02-17-2004, 10:38 AM

Quote:

Originally posted by wbain5280
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.

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!)

BoostnBenz · #5 02-17-2004, 10:49 AM

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.

Jim Anderson · #6 02-17-2004, 12:59 PM

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.

habraken · #7 02-06-2008, 01:06 AM

Quote:

Originally Posted by Jim Anderson

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.

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

dynamitejacket · #8 02-17-2008, 06:33 PM

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?

bgkast · #9 03-16-2008, 10:34 PM

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?

TomJ · #10 03-17-2008, 01:10 AM

Quote:

Originally Posted by bgkast

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?

The fan (easy to test with jumpers, at least at full, 12v setting) or the resistor, located on the firewall, usually pass side in engine compartment.

TomJ · #11 02-17-2004, 05:39 PM

Quote:

Originally posted by dieseldiehard
The root of the problem with these climate control modules is due to the factory designing a mechanical joint that used solder to carry current as well. This is a NASA "no-no." To meet good manufacturing practices all electrical connection interfaces (ie. solder joints) are to be secured with wrapping a wire to a terminal or staking before soldering, that way the solder can't flex and crystallize (a well known phenomena.) Crystallized solder does not carry much (if any) electrical current.
This is not to be confused with a cold solder joint, it is a material fracture.
I have fixed several of these CC units, and the solution is always to resolder the butt-joints where the circuit boards on the sides meet the main board.
I believe flexing occurs when the buttons are pressed, the whole assy receives force that translates as stress on the joints and over time it fractures.
..................

Yep, that makes sense.

Fisherman · #12 04-17-2004, 09:11 AM

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.

BoostnBenz · #13 04-17-2004, 09:28 AM

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?

Mr Goodfahrt · #14 04-17-2004, 09:36 AM

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.

Fisherman · #15 04-17-2004, 03:26 PM

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