I just wanted to preface this by saying that the BEST solution to ACC problems is to properly troubleshoot the system and return everything to factory specs. I did this on my daily driver and there's something really satisfying about having such a nifty system operating as it should. It's also a very good system when working properly!
Unfortunately it can also be an expensive system to rebuild. It cost me about $700 to get mine working
Roughly $500 for a servo, another $100 or so for the amp, a little more for the pods that had failed...
Proper ACC II function relies on 5 vacuum pods, 6 electric/vacuum switches, the servo, an amplifier, a "sniffer" thermistor and enough vacuum lines to circle the globe
Add to that the wiring necessary to keep everything humming and you have a pretty complex system dedicated to keeping your @ss comfortable... I won't even go into the auxiliary water pump which is responsible for so many woes
Neat, but unnecessary...
I've read about everything on the interwebs about the ACC II and I've seen folks go to great lengths just to get some heating or cooling in their cars when the system has gone kaput and left them with either no heat or scorching heat with no control and no air out of the center vent
Solutions have included installing a push/pull knob for controlling water flow to the heater core, which seems rather crude in a Sonderklasse, the infamous UT kit which is expensive and won't help if you have vacuum/pod troubles and some guys who have retrofitted entire switch gear from other cars. Plenty of us lust after the manual systems and dream of doing a retrofit into our cars but even that looks daunting and would probably require a parts car to get it sorted.
About a year ago I started this thread:http://forum.w116.org/mechanicals/altering-acc/msg84573/#msg84573
And since then I've been tinkering with the ACC trying to figure out a simpler/cheaper way of doing it and maybe help some fellow 116 pilots enjoy they're cars without spending a ton of $$ on something as simple as a HEATER!
The first obstacle I ran into was the automatic center vent flap. Here's a peek-a-boo shot of what is required to operate it:
On the far right you can see the passenger side defrost duct. The center opening with the pods above it is the center vent opening with the automatic flap assembly removed. The opening on the left with the flap open is the drivers side defrost opening with the duct removed.
The pink pod on the right is for the automatic center vent flap and the white one is a double acting pod for the defrost. The defrost pod has 2 positions, half open and full open. It's full open for DEFROST, half open when BI-LEVEL is selected, closed for cooling and it's connected to the center vent pod via a vacuum line. It appears as if the defrost pod starts leaking it closes the center vent and opens the defrost flap. It's a safety feature to insure that you'll still have full defrost if something goes wrong.
This was my quick and dirty solution:
I pulled both pods and moved the pink single acting center vent pod over to the defrost position. Now I only have ONE pod and ONE vacuum line running the defrost flaps instead of the THREE lines it had previously. No automatic center vent flap but there is still a manual flap ONE INCH AWAY from the automatic one
The pods are held in by little friction washers that you can pry off with a screwdriver.
I did have to change the metal actuator arm from the white pod to the pink one but it's pretty easy to do once you open the pods up. Sorry I didn't take pics but it's pretty simple to do once you get the pods out.
Here's a picture taken through the dash opening with the defrost duct removed:
This helped a great deal with gaining access to the center pods. It's held to the dash with little metal tabs folded over and you can reach in and straighten them out and fidget the duct out:
It's a 2 piece affair held together with VERY SHARP staples so be careful! You can see the 3 square openings for the metal dash tabs on the top side of the duct. It came out in 2 pieces. It was fiddly but it did come out after some work! I would be leery of trying this if I had a pristine dash in this car because I had to flex the duct up through the defrost openings to get it out and it would SUCK to mess up a nice dash in the name of lazyness! I didn't damage my dash any more but you'd have to be VERY CAREFUL!
Here's a picture of the center vent nozzle with the automatic flap removed:
It's held on with 2 little metal clips on either side. I didn't take pics of the disassembly but it's pretty straight forward. Just remove the registers by carefully prying the retaining pins on either side with a screwdriver and they slide out. It helps to point them down as far as they will go and rotate them downward as you pull them. This will give you access to the metal arm on the "pink pod" and you can separate it from the flap with some needle nose pliers.
After the registers are out you can remove the vent after removing 2 phillips screws on either side and working the rubber boot off the nozzle.
Here are the 2 pieces out:
After working the vent assembly out. (It'll come out through the glove box opening) you can pull the little metal clips holding the nozzle on and wiggle it out.
Now I have normally open defrost ducts that will close with vacuum applied and NO automatic center vent to fail
So what now?
I applied vacuum to the pushbutton assembly and attempted to map it's vacuum function:
The map isn't correct because I neglected to notice that nipples 1,2 and 3 are connected together via the rubber plug that connects to the back
Never assume with MB...
The only switching I had to work with were ports 4,5,6 and 7. Fortunately #6 has vacuum with either OFF, AUTO LO, AUTO HI and no vacuum with BI LEVEL or DEFROST. Since the defrost vent is closed without vacuum I only have windshield air with BI LEVEL or DEFROST and full vent air with AUTO LO and AUTO HI! So far so Good!
The center nozzle with no flap or flap pod:
The vent installed:
You can see the rod that actuates the 2 defrost flaps and the actuator arm through the opening.
Now for blower speed control...
MB designed in another failsafe into the system here:
The green vacuum switch on the left switches power to the blower ONLY when vacuum is applied. The yellow is for the AC compressor. No vacuum here, no blower other than pressing DEFROST. I discovered through my little mapping adventure that nipple # 5 provides vacuum in all positions other than OFF. Great! I just ran it to a splitter and hooked it to the 2 switches behind the glove box.
Now we have air out of all the dash vents and selectable defrost
No automatic center vent so you'll have to reach up there and shut it yourself if you want it closed.
Here's a picture of what's going on behind the ACC panel:
It's a bit sloppy because I'm still in the testing phases but the vacuum routing is VERY SIMPLE.
The black line (#2) is vacuum from the engine compartment.
The purple line (#6) runs to the defrost pod.
The black line (#5) runs to the blower and compressor switches behind the glove box.
The blue line (#4) provides vacuum when either DEFROST or BI LEVEL are depressed. (Same as #6) I'm going to try using it to switch a vacuum actuated heater valve so those 2 buttons will be for heat.
Here's the heater valve part:
It's a valve from a 1979 Chevy V8 PU (About $10) I hooked it into the same line (Purple, #6) as the defrost pod so now the heat valve is open with the panel in either DEFROST or BI LEVEL.
I'm using this:
to switch blower speeds.
It's just an old servo with the bottom half cut off. The water valve part of the servo is what either starts leaking or binding and causes problems. The top portion of the servo is actually pretty robust with little to go wrong. In hindsight, it would have been much easier just to take it apart and cut the little "drive shaft" off. This would have left the metal water valve part intact which would have allowed mounting using the original bracket.