84 300sd compatible Climate Control?

[JohnFitzpatrick]

re CLIMATE CONTROL for 84 300sd...Is 126-830-0285 the only compatible model #, or will 123-830-1285 do just as well?

[ronw123w124]

Yes they are interchangeable, you'll just have to take off the plastic panel at the front of the one with the 123 part number, which is held by 2 or 4 screws. I used it to replace the broken Climate Control on my 300SD.

[ikeepzitclean]

although the unit itself and plugs look identical on the w123 and w126 ACC unit, the internals are different on the boards.. so technically i doubt they can be interchangeable. anybody?

[ronw123w124]

The 123 climate controls works on my 300SD the way they should.

[ikeepzitclean]

i have a w123 and w126 unit and both are 1984.. i plugged them in out of curiosity and they both seem to work, but how come they have diff. internals then? side boards are identical but main and "daughter board" are different (w123 CC has 4 relays things and w126 has 6). im confused now..

[mclare]

Originally Posted by ikeepzitclean

i have a w123 and w126 unit and both are 1984.. i plugged them in out of curiosity and they both seem to work, but how come they have diff. internals then? side boards are identical but main and "daughter board" are different (w123 CC has 4 relays things and w126 has 6). im confused now..

Have you compared the schematics side by side?

I don't have a 123 or manual set for a 123 so I cannot, but if someone does, I can compare them and give a definitive answer.

[ikeepzitclean]

Originally Posted by mclare

Have you compared the schematics side by side?

I don't have a 123 or manual set for a 123 so I cannot, but if someone does, I can compare them and give a definitive answer.

yes i compared the CC units side by side and the 2 internal boards I mentioned above look different and even the 5 switches on each board have diff soldered points..

see pix attached:

left picture - w126 CC is on the left and w123 CC on the right
right picture - fully disassembled w126 CC is on bottom and w123 CC is on top

[ikeepzitclean]

what do u think Mike? cuz i just picked up a few CC's from the JY.. 1 is a 126 and the other's are 123s.

[Grumpy560]

From what I have been reading about the CCU for the W126 is that in the early gen1 there was a problem with the circuit board getting fried when the aux water pump failed thus burning the board up, I don't know if this problem existed in the W123's or not. From my understanding this problem was solved by installing a protective circuit into the CCU itself sometime in the later gen1 models and remained so into the gen2 W126 models until the end of production. I have read this somewhere in a thread but I can't seem to find the same one again.

This would explain why the early gen1 circuit boards look different than the later gen1 boards. I know for a fact that gen1 CCU will not work in a gen2 or the other way around and the gen1 circuit board looks nothing like my gen2 board, not even close.

[ikeepzitclean]

Originally Posted by Grumpy560

From what I have been reading about the CCU for the W126 is that in the early gen1 there was a problem with the circuit board getting fried when the aux water pump failed thus burning the board up, I don't know if this problem existed in the W123's or not. From my understanding this problem was solved by installing a protective circuit into the CCU itself sometime in the later gen1 models and remained so into the gen2 W126 models until the end of production. I have read this somewhere in a thread but I can't seem to find the same one again.

This would explain why the early gen1 circuit boards look different than the later gen1 boards. I know for a fact that gen1 CCU will not work in a gen2 or the other way around and the gen1 circuit board looks nothing like my gen2 board, not even close.

I see what ur saying.. and I know there's a diff. between gen 1 and 2 w126 CCUs. but what we were trying to figure out was the difference between w123 and gen 1 w126 CCUs and if they are interchangeable, which I doubt (based on da internals)