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  #1  
Old 03-08-2004, 02:02 PM
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Join Date: Jul 2000
Posts: 22
80 300D vacuum problem

I will not be defeeted! I have the console out of my 80 300D looking for the vacuum leak source in my climate control system. Here's the deal - I have nothing out of legroom flaps, DEF and BI works, with AUTO HI/LO there is never anything out of the center vents, everything comes out defrost and lateral vents. The strangest thing of all is that I have warm(sometimes hot) air out of the right side defrost while cool (cold) air comes out of the left. None of my resources explain how this difference can occur. I hope someone out there can.

I am trying to isolate this thing using a vacuum guage that shows consistent 20" in defrost and fluctuating 15-18" in other modes.

Thanks for any help.
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  #2  
Old 03-09-2004, 12:20 PM
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Join Date: May 2002
Location: Central Oregon
Posts: 1,004
Sounds like a control valve...

Testing these systems is not as easy as it should be. Do you have the factory shop manual i.e. CD?
There are step by step procedures for testing the systems and it is not very darn easy to test them without starting at square one and then moving through the test procedures one at a time.

If I remember though behind the acc control unit there are several pods that control various functions at various settings. Reading the schematic for these reminded me that I should have paid more attention in shop class but if you can isolate these to their various functions you may be able to exchange one with another and see if this corrects what seems to be erratic behaviour.
Sounds like you may have a pod that is not working correctly or maybe more than one.
Do all the vacuum controllers cycle as you are working through the various settings? Foot vent actuators, dash vents, etc?

The other potential is the dreaded acc servo on thsi year and it seems to be a mystery device as I cannot find any true tests for this unti other than work, no work...
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'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique
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  #3  
Old 03-10-2004, 03:54 PM
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Join Date: Jul 2000
Posts: 22
Fisherman
I am using the diagrams from the CD and troubleshooting instructions from Kent Bergsma's booklet (excellent booklet by the way). I agree on the difficulty of following those CD diagrams. I have identified the pods you mentioned but I am unable to identify the actuators for the leg and vent flaps. the CD info show them where they ain't on my car.
The servo thing intrigues me also. I thought about it when considering different temperature air on each side.
Anything else about locations or the servo would be a big help.
Thanks
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  #4  
Old 03-10-2004, 05:18 PM
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Join Date: May 2002
Location: Central Oregon
Posts: 1,004
it's been awhile since I've been in there...

I believe the footwell flap actuator to be on the drivers side up against the firewall and behind the center section of the dash (if you know what I mean). remove teh kick panel and then dig in under there and you should find it.

vent flap actuator is accessable through the glovebox as i remember. it is on the very top of everything under teh dash I think... To remove the glove box there are several small pins that insert into plugs that fit into the box edges around the front side. Using a small screwdriver pry teh little plastic pins out of the plugs. Both surfaces are on the inside of the box. I don't know how else to explain it but once you do one it will make total sense.
Then remove the light fixture by pulling/prying inward and disconnecting the wires. You can now pull the entire interior of the glove box out.
Gosh, I sure hope this isn't the way to the defrost vents... Sorry if I am having a senior moment here.
I fairly recently helped a friend on his 85 and I may be remembering his layout.

Are you chasing your vacuum lines with a MityVac? I had one line that went to the acc control unit that had a bad rubber connector and this was at the root of all my problems, I thought. After I fixed this all my flaps etc worked but no heat still. That's when I figured out that it was the servo on my car.
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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

Last edited by Fisherman; 03-10-2004 at 05:32 PM.
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  #5  
Old 03-10-2004, 10:10 PM
Bailey'sBenz
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LOOK AT THE LINES BEHIND THE BATTRY !!!

I had the same thing happen to my 1980 300D about 6 years ago. I had the time to put the car out of commission for a while and did so. Decided to get the M/B A/C systems manual and got to chasing down the problem. Once I had the dash and center system out, I decided to take it a few steps further. Knowing that North Texas is no place to be without a reliable climate control system in the car, I went ahead and replaced all the vacuum actuators and switches. It wasnít that hard of a job, nor very expensive. Remember also, that you can replace just the diaphragms on the vent actuators without having to get the whole thing. Knowing I was running the original servo, I replaced it also. I still had the problem you have when I was done with all that.
Hereís one place you might not think to look. But, where I found my problem to be. Pull the battery and split the case on the bundle of vacuum lines running into (and out of) the car from the servo. Seems battery fumes can get into that casing and rot the plastic vacuum lines. I had two of the lines just crumble as I pulled the sheath back from them right by where the battery sits. The casing/sheath looked fine. You have to look DEEP inside. Clear into the area behind the glove box. I tried to repair the lines by cutting and splicing with tubing. That showed for sure where the problem was, as the system worked fine after that. At that point though, I decided to just buy a new vacuum harness and install it prior to putting the whole thing back together again. Someone had told me that replacing much more than an inch of the hard vacuum tubing with rubber hose was not a good idea. So in went a new vacuum harness. About 125.00, I think it was.
I also converted to 134A at that time.
Another thing to keep in mind is the quality of your coolant, and the fact that it runs through the bottom valves on the servo. Any crap in the coolant seems to jam things up in the servo, and thatís not a good thing at all. Jam the bottom valve and you stop the vacuum valving that goes on up top.
I change and flush my cooling system every year. I pull the lines off the bottom of the servo and flush it out real good too. Once a month, no matter what time of year it is, I run the system at max heat as well as max cool for a few minutes. Iíve not had an A/C issue since.
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  #6  
Old 03-10-2004, 11:44 PM
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Join Date: Aug 2002
Location: NE Okla
Posts: 1,104
herbct01,

There is some good info on both of the links below. Yes there was a Chrysler .. MB link long before the merger. Imperials used the same Servo based HVAC control system as our pre 82 MB's.


http://imperialclub.com/Repair/Air/index.htm

On the second one, click "restoration tips" on the left.

http://www.duricy.com/~imperialist/
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  #7  
Old 03-29-2004, 11:40 AM
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Join Date: Jul 2000
Posts: 22
I got it! Nothing to brag about though because had I have gone there first I would not have had to pull my interior apart.
My problem was corrosion in the vacuum line bundle at the battery. This area had been found by a mechanic and repaired a few years ago and I was not led to this area until I started using the MityVac to test the lines out of the servo. First the audible leak and the rest was opening up and splicing, or resplicing, some broken or corroded lines.
Looks like some acid was left in the bundle after the splices were made and the orignal harness was reused.
All my symptoms are gone. My climate control works as designed, the engine shuts off right away and the door locks are working 2 days later.
Thanks to all for your insights. The books on this vacuum sytem that I ordered from **************.com were invaluable.
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