more of the hated climate control servo - PeachParts Mercedes-Benz Forum

Wiz3D · #1 12-05-2006, 12:01 PM

'Tis the season to be cold, even in SoCal ... and, of course, the heat and defrost stopped working on my 78 300d. I have read every thread I can find on this site regarding this problem but I haven't seen what I think I need. More on that later. I do remember, while working at the dealer when these cars were new, that we handed servos out by the dozen. Question is, what do I need to fix first to get back the heat and defrost? I'm saving the AC for a later date.

Little background; heat and def worked fine ... temp wheel adjusted the temp and it blew at the right places and times ... until this spring ... until just after a citric acid flush. Soon after, a rust spot came through the little metal bypass pipe between the head and block. Uh-oh? Then, soon after that, the aux wp quit. Replaced it. Then the blower stopped working. Was just simply, finally dead and I replaced it. I know by feeling the heater core inlets and pipes that no hot water is getting into the h/c or even getting by the servo on the hot water inlet side. Hmmm .... I pulled the servo off and it looks good from the outside EXCEPT for the customary crack in the center body of it. Can I check this thing off of the car? I already know from taking a spare servo apart that I may not be able to get it back together again so I'm reluctant to dismantle this one without a known method or diagram.

Does a crack, which is not leaking water, mean that the servo's shot? There was noticable release of vacuum from hoses (the reservoir) when I unpluged the lines ... so the servo's not a likely source of a vacuum leak at least when the car is shut off.

Secondly, does anyone have, or know where to get a diagram of the innards of one of these things?

Looking at the 123 CD rom, I'm not even sure I can test for what the defect is if I don't have a spinning compressor?? Man, I wish I had my old blue shop manuals back ......

Hunter, Brian and guru's all .... how do I go about fixing this issue PDQ without buying a new servo or an "Unwired" replacement? Funds are scarce as I'm disabled with low vision now ... but I do have a couple of parts cars, a slab to work on, lotsa' tools, time, a fair amount of skill and the will to do it.

Mr.Kenny · #2 12-05-2006, 12:09 PM

http://www.imperialclub.com/Repair/Lit/Master/281/index.htm
have fun!

rhodes2010 · #3 12-05-2006, 03:58 PM

I drive a car that uses the same setup.
You seem really well versed in all the aspects of this thing.

The short answer: Get a piece of hose and bypass the servo,
Go straight from the auxiliary pump to the pipe on other side of servo.
Hot water all the time. If you want, add a simple ball valve in-line to
shut it off when the dayimte temps finally come up a little.

Long answer: Get the replacement aluminum servo and a new servo amp
(behind the glove box). Or pay the larger amount and get the no
servo replacement.

I drove for 3 or 4 years with a bypass hose until finally got after getting it to work.

I had to remove the battery and replace/re-run/repair all the vacuum hoses
next to the battery, they had all hardened and cracked and leaked.
What a pain, but worth it.

The Chrysler group has the most excellent write up on how this thing works.
Very precise in describing each connector, line, and wire for operation.

http://www.imperialclub.com/Repair/Lit/Master/281/cover.htm

They describe a piece of test equipment for these systems.
I was able to acquire the Chrysler Auto Temp II version and am working
on making an adapter to connect it to the Mercedes harness.
But after all that, I think most problems can be solved without it.

Wiz3D · #4 12-05-2006, 06:02 PM

Thx to the repliers .... I'm printing the Imperial book on the system ... that'll take a while on my dial-up connection. Cool though. A beautiful, simple look at ACC II. I did read in there that you can't service servos in the field because of special assembly tools needed. I fiddled away the entire day yesterday makin' little jigs and such while tryin' to put one back together .... all to no avail ... so that's a stopper, I guess. I still wonder if it is possible to test the servo functions, or some of them, on a stand-alone basis outa' the vehicle???

Does anyone know if that open crack in the side means that the unit won't work at all or won't work correctly OR doesn't matter much or even matter at all?

Of course I will eventually bypass it with a hose and ball valve on the heat side if and when I discover that I'm 'p----ng up the proverbial rope' ... and I think I'm almost there. Thx again ....

Wiz3D · #5 12-05-2006, 08:17 PM

Thx to the repliers .... I'm printing the Imperial book on the system ... that'll take a while on my dial-up connection. Cool though. A beautiful, simple look at ACC II. I did read in there that you can't service servos in the field because of special assembly tools needed. I fiddled away the entire day yesterday makin' little jigs and such while tryin' to put one back together .... all to no avail ... so that's a stopper, I guess. I still wonder if it is possible to test the servo functions, or some of them, on a stand-alone basis outa' the vehicle???

Does anyone know if that open crack in the side means that the unit won't work at all or won't work correctly OR doesn't matter much or even matter at all?

Of course I will eventually bypass it with a hose and ball valve on the heat side if and when I discover that I'm 'p----ng up the proverbial rope' ... and I think I'm almost there. Thx again ....

cconbalsam · #6 12-05-2006, 10:27 PM

I don't think it is a good idea to simply bypass the servo by splicing in a piece of hose and a ball valve if your auxilliary water pump works. If you do this and run with the ball valve closed the aux pump will be deadheaded and may be dammaged. The servo, when closed, bypasses the coolant back to the return line to prevent this. I would install 2 t's where the servo was and attached a smaller line between the t's. The t's, fittings and extra lines would be cheaper than a new aux pump.

rhodes2010 · #7 12-06-2006, 02:42 PM

Quote:

Originally Posted by cconbalsam

I don't think it is a good idea to simply bypass the servo by splicing in a piece of hose and a ball valve if your auxilliary water pump works. If you do this and run with the ball valve closed the aux pump will be deadheaded and may be dammaged. The servo, when closed, bypasses the coolant back to the return line to prevent this. I would install 2 t's where the servo was and attached a smaller line between the t's. The t's, fittings and extra lines would be cheaper than a new aux pump.

You are probably right. I tended to unplug the aux pump when heat not needed.
The connector is right there and is really easy.