CCU differences? - PeachParts Mercedes-Benz Forum

Chadahar · #1 12-19-2007, 01:03 PM

I am having some issues with the CCU after burning two up I disconnected my AWP (Auxiliary Water Pump, its DEAD, DEAD, DEAD).
Rebuilt the Mono valve and it is working well.
Installed another used CCU and the heater blower(brand new after market) worked and also so did all the switches.
Drove around and the heater worked, but I noticed when the temp wheel moved cool air came from the heater vents.
Maybe it was trying to Automatic adjust to the new temp but I find that hard to believe.
On max heat it did fine, but anything off max heat got cold air through the heat vents.
When I got back to the house I decided to try to see if the recently recharged A/C was working.
I punched the full air out all vent button and rolled the temp wheel to max cool and everything went dead.
No blower on any setting or speed and the buttons didn't work either. Fearing another smoked CCU.
I pulled the CCU out and took it apart expecting to find burned traces.
There were none and the CCU is fine, but I did notice that this CCU is vastly different inside that the other two.
This CCU has only 5 relays inside instead of 6, and the traces are actually thick solder and not the sandwiched copper traces of the other two.
Also there is only one circuit board in it, not two, the part number on the box is the same.

I checked for burned out fuses and found none. Also the large separate fuse on the fender well is fine.

Now My dilemma is what is not allowing my heater fan motor to work I have replaced the heater relay and the temp relay, but they were used units as well.
Which of the Ice Cube relays are the A/C-heater relays.
I'm about at my wit's end on this.

Also where on a w126 380SE is the aspirator motor found? I have looked beside and behind the glove box to no avail. Is it in the heater assembly box?

Thanks in advance for any help. This is about the last little niggling thing to fix on this car.

brandlj · #2 12-20-2007, 04:17 PM

You do not have an aspirator motor on the 84 380se. That started in 1986. Your inside temp sensor is hooked up via a rubber hose to a nipple that is on the blower motor housing.

Also, up to 1985 you have an older style CCU. I have never opened up one of these before, but I have opened the one on my 86 300sdl and it has two circuit boards.

I do know on the older CCU units there is no provision for a short in the system anywhere, and then you burn a trace on the CCU board. On 86 and later there is a built in circuit breaker that will trip and put the unit into default ( defroster mode) when something in the system goes wrong.

I would check the resistance of the heater core temp sensor and make sure it is in good shape along with the resistance of the interior temp sensor.

Good Luck
I fought a week long battle with my 86 and I won and it works well now. I replaced the monovalve insert, the center vent pod, and the CCU.

John
86300sdl

Chadahar · #3 12-20-2007, 06:12 PM

Thanks John,

I opened up the original CCU that came with the car(PO's had not replaced it) and it had the two mother boards and two wing boards. The PO had not disconnected the mono valve(bad) or the AWP (bad) so they fried the original unit before I got the car, along with the help of a dead heater blower motor.
The CCU in there now is, as I said, one mother board and two wing boards. It probably died too. As my heater(monovalve(either plugged in or disconnected),gives heat through the defroster vents and the lower dash vents.
The original Heat sensor (cabin) smoked and I replaced it with a used one. I need to remove it and test it too.

All this points to an incorrect CCU, or maybe some of the electrical components blew as the only heat I have is defrost and only if I'm moving. None of the traces are burned through, but the one less relay and the one less mother board concerns me.

I'm a bit P.O.'d in that a couple used parts I just bought were useless. I will inform the parties concerned. I don't mind buying used parts if they are as represented. Good means good and working, not just all there. As in a used AWP that had the armature rusted to the field magnet. No way in heck that was EVER tested.

So back to the drawing board. Get a good Soldering iron and try to fix my original CCU. luckily it has just two burnt traces, easily fixed. Wish I had found the correct AWP plug and disconnected it when I first read these will fry the CCU. I unplugged the mono valve instead.

I'll check both of the parts you recommended.

I am more than a little disheartened.

Strife · #4 12-20-2007, 08:23 PM

there is a wiring difference between <86 and 86+ 107 CCU's, and this was probably a corp-wide change. I don't know if they are plug interchangeable, but they are definitely not electrically interchangeable, and the 86 is not "backward compatible".

brandlj · #5 12-20-2007, 09:33 PM

When I did my work this weekend, I went to the ProGrama website and clicked on the CCU for my 86300sdl. There was a wonderful troubleshooting guide on how to check the monovalve, the awp, and all of the sensors using a VOM. This was all done by measuring thr resistances at the plug in connections on the CCU wiring harness. It was really easy. Go check their site and it may help you.

I found that all my sensors were within spec and my awp was also within spec. I also applied 12 volts to the awp connector under the hood and listened to my pump run. I found my monovalve ruptured, I found one vacuum pod bad( the one for the center vents) ( man was that a bear to replace) and I found my CCU bad.

I had another in stock in my attic. ( I get them from junked cars in the wrecking yard.) I plugged everything in and it worked.
By the way, I also have a very valuable book that I purchased from Mercedes back in 1990. It is the Climate Control Manual in print. It covers 1981 thru 85 and then revisions for 86,87,88. This book was invaluable for resistance readings specs on the different sensors, and instructions on how to replace the different pods etc..
If you ever come across one on E-Bay, snatch it up!!!

Good Luck and if I can help you somehow, drop me a line

JOhn

Chadahar · #6 12-20-2007, 10:34 PM

Wow! more than I ever realized about climate controls and the different models. My 1984 380SE takes 126 830 0285 (60285)
(ProgRama's number?)model.

The CCU's I have are this model.....at least the cover panels are the same MB number. Now I know for sure that I have at least two different configurations, two with a mother board,a child board and two wing boards (each have 6 relays) One has only the one motherboard and two wing boards. (5 relays). This one appears older than the other two.

I will doing the ProgRama tests this weekend. Then I should know where I stand.

I may send my original (best shape) CCU to them for a rebuild. Only two traces are burned through on this one. and from the diagrams it was the AWP that fried it. I'm going for a NEW AWP and I'll rebuild my Monovalve also. My AWP is dead as is the one I bought to replace it. GRRR! Monovalve does work when the CCU is working. It now is in the open mode(defrost).

Someone provided parts of the Climate control manual on this site or another and I downloaded that part. it was not complete, but it did have all the diagrams.

Thanks for the help John. I feel much, much better now.

CONRAD · #7 12-23-2007, 08:07 PM

Hi John.

Could you send me copies of the references you are referring to
about the CCU and even pix of how to ' R&R ' the CCU ?