126 ACC Unit disassembly - PeachParts Mercedes-Benz Forum

AUDIBLE · #1 01-20-2012, 03:39 PM

1987 300SDL

Later ACC unit with the large "auto" button.

I've read the threads and seen the instructions for resoldering the older ACC unit with small "auto" button. The later 126 ACC with the large "auto" button is a very different design, where the temp wheel is NOT part of a module that just pulls off. I'm trying to get this temp wheel off so that I can remove the board and get to the relays underneath.

Can anyone tell me how to either get this wheel off, or how to otherwise remove the board?

Attached is a pic of the wheel I'm trying to get off.

thanks!

ah-kay · #2 01-20-2012, 03:51 PM

I have not taken the wheel off the ACC unit for W126. But on the W201, you pull the pin on the side ( hex shape at the center of wheel ) and it will pop out. It may be a bit tight.

AUDIBLE · #3 01-20-2012, 05:47 PM

Pulling the little hex pin did the trick, thanks.

Of course, once I got the wheel off and could see inside, I found I didn't need to bother. Unlike the earlier model, there's nothing user-serviceable in there. Just a board with a bunch of electronics instead of relays and diodes. Plus the board is STAPLED to the ACC chassis, which tells me that if re-soldering doesn't work, then the ACC is toast. Have others found this to be true?

thanks
Bruce S

compu_85 · #4 01-20-2012, 06:14 PM

What was your system doing (or not doing) before?

-J

AUDIBLE · #5 01-20-2012, 07:35 PM

As relates to the ACC, it had no reliable control over the heat or AC. Different button-pushing sequences would sometimes get the desired heat or
AC, sometimes not. Tapping on the front of the control panel would sometimes start the heat. Defrost would sometimes have heat, sometimes it would have heat when turned on, then cool off as air went over the heater heat coils. (Mono-valve rubber is torn, needs rebuild as well. Most of the things I've read that have been diagnosed as a bad ACC it's been doing.

thanks
Bruce

ah-kay · #6 01-20-2012, 10:57 PM

Quote:

Originally Posted by AUDIBLE

(Mono-valve rubber is torn, needs rebuild as well.

thanks
Bruce

If the mono-valve is torn then the valve could stuck in the fully open or fully closed position. It is kind of random as the rust gets inside the plunger and it could jam the plunger in either positions. It happened to my SDL with no heat or no A/C, depending on the mood of the car. I would recommend you to change out the mono valve plunger first. There are plenty in the JY from old gasser. Then look at the ACC unit if the problem still exists. Good luck.

AUDIBLE · #7 02-13-2012, 09:40 PM

I "rebuilt" the mono valve with new kit. It improved things to the extent that hot coolant is now getting to the heater core reliably. I also took the ACC unit out and resoldered everything that could be resoldered. I'm not sure that the resoldering did any good, or if I may have left something disconnected, but the AC compressor doesn't engage (it already didn't before I started the ACC repair) & the air flow/output to vents is still not correct. So I'm pretty sure I have a vacuum problem to work on, in addition to the AC system itself.