coolant leak/black box

[floydo]

Hi all,
This is my first Diesel. She's a 1980 300TD Wagon with 308,000.
I have a coolant leak. It's pretty consistent, and by keeping an eye on the thermometer, and adding when necessary, I can keep it running between 80-100°. Mostly I'm waiting for a warm enough day to change the hoses. But looking closely at my leak, I found that it seems to originate at the bottom of the black box in the photo. That is, the leak seems to come from above the hoses which run to the bottom of the box. I can't find a picture of that black box in my Haynes, so can anyone tell me what it is? I'm planning to drain the coolant and change the appropriate hoses, but might I need to replace that box too?
All help appreciated.
Darren

I can't get the add image thing to work, so please look at the images here:

http://homepage.mac.com/humiliated/PhotoAlbum1.html

[kerry]

You have a leak in the dreaded ACC servo. Simple to replace but not that cheap. You'll want either a cheap used one from a junkyard (real cheap since it is likely to fail also) or a rebuilt or new one with a metal body as opposed to the original plastic body. The cheapest I have ever seen the rebuilt metal body ones is $289 from Randy at European Parts Specialists 805-683-4020. Someone posted a few weeks ago that all the rebuilts are out of stock.
you can find some comfort in the fact that anyone who owns a pre-81 300d is intimately acquainted with this servo and on sleepless nights has a regular routine of cursing the engineer who came up with them. My guess is that since all the 300d's that came to the US had them, the engineer was a WWII POW trying to get back at us for having to eat Spam.

[floydo]

Thanks Kerry,
for your quick reply. So I've read some of the past threads on the ACC Servo and I'm a little more confused. I also don't get heat blowing in any setting, even though I can feel the heat in the dash while driving. Plus my passenger door and wagon door do not lock with the vacuum. So these vacuum and heat related problems are possibly connected to this thing which is leaking coolant? It seems that most people try to track down the problems elsewhere until they conclude that the servo needs replacing. But since mine dumped a ton of coolant in this recent cold spell, does it seem reasonable to replace it first and hope that it helps my vacuum and heat situations? Or is that naive?

Darren.

[tryan]

try george_murphy@compuserve.net. not sure if thats the right e-mail. he is a mbca member that has ads in the star.

[kerry]

There could be a vacuum problem in the servo leading to other problems but I doubt it. I would replace the servo because it is leaking and troubleshoot the rest afterwards. The lack of heat problem is likely related to the malfunctioning of the servo since it is the servo that opens and closes to allow hot coolant to flow. It also is the brains of the vacuum part of the heating system (I believe)
George Murphy does sell metal bodied servos with either new parts or rebuilt. I think the rebuilt run around 395 and the new around 495. Do a search here if that e-mail is not right because I know it has been posted before.
I would suspect that the door problems are bad vacuum diaphragms inside the door. Not that difficult or expensive to fix.

I have one of those servos too. I would love to find the engineer who created one of Mercedes "better ideas". I have found several rebuits from http://www.germanstar.net and I found an orginal oe type from somewhere, it was brand new; however, it had a 950$ price tag. I have solved the problem of not getting any heat, bypassing it totally. But the true test is going to be this summer when i probably don't have any a/c.

[floydo]

So Randy got back to me with $329 + $75 core charge, which I didn't really understand. German Star also had the metal body for $365, which I'd already ordered by the time that Randy called back. I never did try to contact George Murphy, but both Randy and the guy at German Star were very helpful and friendly.

So, now that the part is coming, I'm trying to figure out how to install it. My MB cd, which is a badly made copy, seems to call the ACC Servo the "regulating valve". Can someone confirm that? I'm looking at 83-632 from the cd. Looks simple enough. Randy mentioned something about "check the amplifier" implying that I could hurt my new ACC Servo if something is wrong in the amplifier. Does anyone understand that reference?

Thanks for all the help, somehow $365 doesn't seem so bad after thinking about $950.

Darren Floyd

[jcd]

Replacement is fairly easy,,,,,just keep track of how you take the old one off and put the new one on the same way. This is a good time to flush and replace the coolant, since you're going to have coolant all over the place anyway. Also check the hoses and the clamps as well while you're at it.

Kerry is exactly correct. Replace the servo and you'll see a major improvement, then you can attach any other vacuum leaks.

JCD

[Fisherman]

I had already flushed my coolant so wanted to save as much as possible. I made four tapered wood plugs so taht I could seal off each hose as it was removed. I think you can get round wooden stakes at the local lumber yard that would do the same thing.

Here's my way to do this changeover if:
your car matches my 1980 300D
you want to conserve on lost coolant
you have the patience to read my post...
You resolve to not hold me liable for anything ever!

Leave the radiator cap ON to limit coolant loss.

Disconnect the vacuum block mounted to the top of the servo by removing a single set screw that is mounted on the back of the vacuum block in the middle of all those vacuum hoses...
Once the screw is out just gently pull the block straight off the back of the servo...

Disconnect the two wiring harnesses by lifting up on the backside (they have keys that fit into a slot on the back of the servo) of them and pulling them away from and therefore out of the servo.

Next undo the hose clamp on the auxillary water pump or whatever is being used to hold it to the bracket. then remove the coolant line connecting the pump at the servo. This line needs to be plugged when removed and the servo will leak a little coolant but not much through this connection.

Next undo the hose clamp on the opposite side of the servo (firewall side) and be ready for some coolant flow. Plug this hose off. It is the main feed to the heating system.

Next loosen both remaining hose clamps but do not pull the hoses. Once you have them both loose remove the front hose and block off this line while simultaneously holding your finger over the servo connection to stop the water flow. This is the main engine return side and has a flow through opening in the servo that allows water through all the time.

Now remove the last hose and plug that line....

Installation is the reverse of removal with one caveat. Some folks say that it is best to put an inline fuse in place on the auxiliary water pump becasue they have been known to seize and when they do can backfeed to the controller and short it out. I have no idea what amperage to use for this as I cna find no spec on the pump other than that it is there...
Not a bad idea and without the servo there you have lost of room to work.

Now have a beverage of your choice and hope for the best...

The CD has about thirty pages of testing on this subject from which very little is valuable information unless you have vacuum leaks all over the system. In which case you have to pull the center console to get to the stuff to be tested. If you ever go this route IMHO pull the seats first. They are only held by 4 bolts and the added room is really nice to have when working in there.

If you'd like to run some tests on the system I now have a pretty good understanding of it after digging around in it for two days. send me a PM and I'll try to explain all the steps that I did before just trying a new/used servo.

BTW - testing the amplifier is done via the info on the cd (resitance values given) and there is a 10 pin plug mounted up next to the firewall (at least on my car) behind the blower. You need to know what pins to check and the readings you should see from the CD.

have fun....

P.S. sorry for the long post.. how about a DIY award...

[floydo]

some new hoses, and the great tips you guys have given me, I went out today to take care of this dreadful leak. But I couldn't find the drain plug for the radiator. Actually, I found it, but instead of the screw that the haynes shows, I have a half-finger-length hole which has a smooth plastic feel where I think the drain should be. Actually I have two such holes, one on the right and one on the left. There's nothing to screw, nothing to pry, just the holes. Any suggestions?

[kerry]

I couldn't find a drain plug on mine either. I just loosened the lower radiator hose.

[Kyle Blackmore]

The drain is located at the mounting lug (on the driver's side I think).If you don't have one there it might be an aftermarket rad,pull the lower hose if you have to.Someone mentioned the amplifier and it is worth it to check it and resolder if necessary.I had a bunch of weird ACC gremlins that went away after I resoldered the amp,it may have caused the servo to screw up in the first place.I never tested it , I pulled the glove box out ,removed the mounting screws and unplugged it.When I opened it I found dark staining on the solder and one resistor was loose.I carefully resoldered the board and it's been fine ever since.BTW I think the servo was cheaper here in Canada (at the dealer)around $400 Cdn,but don't quote me on that . Good luck.

[floydo]

so I finally put the new ACC servo in my 300TD wagon this past Saturday. It was a bit of open heart surgury, hoses and gushing fluid, but it's all back together and so far no visible coolant leaks!

Thanks for all the help Gentlemen.

I haven't noticed any significant changes in my climate control situation. The previous owner said the heater used to run all the time, until it stopped. Maybe this summer I can track down the heating situation, b/c I can't do another New York winter with no heat.

Floydo

[Fisherman]

There are a couple of very straightforward tests you can do to the system without much work to see if it is functioning.

1. Start the car when cold and turn the control panel to defrost. if you get blowing you are halfway there...
2. Turn off the controls and then turn them back onto low or high setting. The system should not come on or blow until the car gets up to about 100 degrees f.
3. Once the system starts blowing (or doesn't in which case you can go back to the defrost setting to make it run) place a screwdriver onto the aux water pump and listen to the end to "hear" if the pump is running. If this pump doesn't run you won't get heat...
4. If the system did not start when the car warmed up then check the black vacuum hose that tees off to the bottom of the acc servo for vacuum. If there is no vacuum here or on the other line (yellow I believe) coming off the bottom of the acc servo then you have a major vacuum leak in the system or no source vacuum getting to the system.

My system had the main vacuum line at the controls in-dash that had come loose and was just hanging there. Obviously this caused some problems...

This is my .02 test process...

Let us know if things start working or what you find during these tests.

[floydo]

Ok.

So the heater never comes on, no matter what.
I put it on defrost, I put it on anything, I change the temp dial, it never comes on, it never even makes a sound.

But, while driving, the car does make heat, and the heat is evident in the dashboard vents and the defrost vents. It's doesn't "blow" around, but when the car's moving, it does keep the window clear even in Winter. But, my feet freeze.

Since I just replaced the ACC Servo because of the coolant leak, I know that the vacuum connections from the bottom are good.

What next?

Floydo