So I took out the ACCU and resoldered the parts where the solder keeps the two board together. It worked great for the first three times I started the car after that, then I let it sit for a few hours, and went out again. This time it didn't work. I made 3 stops, and restarted my car 3 times, and it didn't work any of the times. On my way back home I remembered something about someone getting it to work by hitting the wood panel in front of the ACCU, and I did that, and the A/C came on.

Any ideas?

__________________
Gabriel
'91 350SD 162k
'83 300SD 210k - rear-ended and scrapped
'84 300SD 210k - totalled

Yea I used to hit it as well. I went through and resoldered everything, it fixed all the problems.

__________________
Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

I was gonna resolder everything, but I don't see the point. I mean, I understand why the sides would need to be resoldered, because all the stress from 20 years of the buttons pushing that board would break the solder joints.
What I don't understand is why the regular solder joints would go bad, and more importantly, why hitting the ACCU would make it work. That second one especially boggles my mind.

__________________
Gabriel
'91 350SD 162k
'83 300SD 210k - rear-ended and scrapped
'84 300SD 210k - totalled

Because internally one of the solders have broken free but don't always make contact. It sounds like you have the exact same problem I had, perhaps you may think it'd be pointless to resolder all of them but it fixed mine. I was told that over 50% of failed CCUs fail in the pins on the side of the CCU, the rest is normally where the buttons are soldered onto the boards and the others are where the side boards meet.

__________________
Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

Just to wrap up the thread... I resoldered almost every pin on the ACCU and the A/C has worked great for 3 days now. I found a few cold solder joints on the boards, and I'm guessing that's what was the problem. Thanks everyone.

__________________
Gabriel
'91 350SD 162k
'83 300SD 210k - rear-ended and scrapped
'84 300SD 210k - totalled

I had similar symptoms... was a combo of Monovalve, blower motor. and cold solder joints on climate control unit (I had em' all).

RepairFlix has good videos on monovalve repair, climate control repair, etc. If you buy direct from his website and not through ebay he will combine shipping on multiple videos.

http://www.repairflix.com/cart.php?cat=Misc+Mercedes+Procedures

Scroll down to "Climate Control Computer Repair"

AND...

The blower motors are expensive, but very fixable... brushes need to be replaced. Easy
Mercedes Source has a manual including the brushes which fixed up my 1982 300D blower motor. Mine also was intermittant.

http://www.**************.com/

Description of the kit (Manual only also available)- (BTW, Fastlane doesn't sell these brushes...)

123/116 Heater Motor Repair Kit
Item # MRG-123HMR

For all 123 chassis cars made from 1977 to 1985 and all 116 chassis sedans built from 1973 to 1980.
This repair guide will take you through the process of how to properly remove your heater blower motor and replace the motors two brushes. This is the most common reason for failure. If your blower motor has been intermittent or some days it won't come on until you drive for a while your motor brushes are most likely at the end of their life. This is something you may just want to replace as a preventative measure. 20 year heater motor brushes are very prone failing at any time. If it has not failed yet it most likely will sometime soon. Along with this detailed instruction guide I will provide you with a set of new brushes (which I have diligently sourced). You will need a soldering iron and a few common hand tools to complete the job. If your car has a over 150,000 miles on it or you know the heater motor has been run a lot, the best time to do this job is now! Don’t wait for it to quit on you on a cold winter morning.

PS... congratulations on tackling the fix yourself. THIS BOARD IS GREAT!

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Mr Goodfahrt (pronounced FAIRT... means "good trip" in German)

1982 300D Turbo Pastel Gray (off-white) 200k+(?)
newbie but willing

I've been reading all these post and my what complications of the heating and a/c units of these MB's. Well in the winter my heater wouldn't work until i drove it about 20 miles. It starts a clicking noise under the dash on the passenger side. Does this for about 5 min. then MAYBE my heater will come on. Now that Spring has arrived and I use my A/C some. The A/C works fine, but when i get out of the drive the clicking starts up again and does it for about 5 min. Is this the climate control that's making this noise? Where is it located exactly? What is the cost in repairing at a local MB shop?

You have a bad pushbutton unit. Shop is gonna charge a couple hours labor and about $300 for a rebuilt PBCU, $500 or so for a new one (they will charge list price).

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Worn brushes in the fan motor can cause mysterious symptoms. After dismantling/checking/resoldering most under-dash components to no remedy, I pulled the blower. It seemed to run fine on the bench, but was still intermittent in the car. Replaced the brushes with some I picked up at the vacuum cleaner repair shop for a buck each (sandpaper to fit) and everything worked geat. - Jacob

I have the CCU out, on my workbench, all of the buttons removed, the bottom cover off, but I do not see how it is possible to get the plastic cover off to access the top without breaking something. Does it just require alot of force, or is there something obvious I am missing.

fyi -
1985 300DT. This whole fiasco started when things went from good to "hot only on defrost". Upon inspection, the hose for the temp sensor had, predictibaly, deterioriated. I put the dash back together, but now the heater fan does not work, even on defrost. High - Low ALWAYS worked before, but the center vents have never worked. I assume that the CCU needs to be resoldered, but how to get at it without shattering it to a thousand pieces?

Have you used the climate control test sequence in the FSM yet? I found it to be extremely helpful.

__________________
http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

Maybe this will help.

__________________
Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

The commutator (copper thing the brushes ride on) on my blower motor was so worn that there was no point replacing the brushes. I was surprised the motor still worked at all. I shopped around and found the best deal to be ******** Arizona, $85 for a new motor and free shipping over $50. The motor is here, it's a new Bosch, just like the old one. All I have to do is press off the fan, put it on the new motor, and be good to go...after I resolder the ACC board of course...having already kitted the mono valve.

The re-solder job, by the way, is the same procedure recommended for the cruise control brain, and works just as well, at least it did for me.

Jeremy

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

I haven't found this - link please

I found my intermittent problems were caused by bad contacts in the ignitions switch. Jiggle the switch and the blower comes on. Might be repairable but I'm going for new replacement.