Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Tech Help

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 02-20-2006, 02:03 PM
Registered User
 
Join Date: Nov 2004
Posts: 20
Climate Control Trouble in a 6.9

When I used my '78 6.9 two weeks ago, it was blowing very hot air regardless of the setting of the temperature dial. I checked the resistance values of the rheostat there via the 10 pin test connector (pin 9 and 10) and saw a resistance of 550 Ohms at 65 F selected and 1700 Ohms at 85 F selected. I then took the car for a test drive.

Now, it only blows cold air all the time, regardless of temperature setting. So I wondered if the servo is stuck. The car has an aluminum bodied servo, and I thought those were more trouble free. Feeling the auxiliary pump I noticed that it seemed operational (slight hum), the lines to the servo were hot, but the lines from the servo were cold.

Any suggestions as to where I might look next? Thanks!

Robert

Reply With Quote
  #2  
Old 02-20-2006, 02:19 PM
Registered User
 
Join Date: Aug 2004
Posts: 232
I think aluminum bodies are less prone to leak, but their likelihood to stick is probably the same.

Yours sounds like it is stuck.

There's a lot of information here about servos, but most will say that when they begin to fail, they don't suddenly get better.

I'm on my 3rd servo (this one is aluminum) in 10 years of 6.9 ownership. When this one breaks, I will be getting the electronic replacement from unwired tools.

The manual at the w116.org site has the test procedures and troubleshooting steps. Look at mercedesshop Vintage/helpful links/116.org/handbook
Reply With Quote
  #3  
Old 02-20-2006, 03:16 PM
Registered User
 
Join Date: Nov 2004
Posts: 20
Thanks oxymoron - I do actually have the w116 chassis HVAC manual, and I just did a quick and dirty look to see if the rheostat was at fault. I discounted the servo because the thought the aluminum bodied ones were a final solution. It appears I may be mistaken. I will follow the procedure more closely and verify before I drop $500-700 in a new servo or the unwired replacement kit.

Besides the aluminum servo, my 6.9 has recently had its radiator rodded out, and new hoses all around to cure an overheating problem. I guess the crud that got the radiator also may have gotten the servo.

Does anyone besides Performance Products carry with unwired kit?
Reply With Quote
  #4  
Old 02-20-2006, 04:46 PM
Registered User
 
Join Date: Aug 2004
Posts: 232
you can buy direct from unwired and I see them on e bay as well.
I sent somebody here on the board some internals from one of my old servos a couple of months ago. some of the innards look stout such as the gears and some are tiny springs.

my first servo bit it when the PO used some Stop Leak and the whole bottom of the mechanism clogged up. it doesn't take much foreign material to mess one up
Reply With Quote
  #5  
Old 02-20-2006, 05:06 PM
Registered User
 
Join Date: Jun 2005
Location: NJ
Posts: 1,182
It is only fair that people driving 6.9s (and 6.3s) don't get cooling/heating air!
__________________
82 300D....went to MB heaven
90 350 SDL....excercising con rods
Reply With Quote
  #6  
Old 02-20-2006, 06:53 PM
Registered User
 
Join Date: Dec 2000
Location: Battle Ground, WA
Posts: 576
Digital servo upgrade...

Hi there,
If you go to the SL forum there is an advertisement for the unwired tools digital servo at the top of the page. It is worthwhile investing in, as it cures the servo problem forever, at least a lot longer than 3 years! My 450SL had the aluminum bodied servo in it, but the gears, etc above the thing were all corroded away. I installed the digital servo and am very happy with it.
The unwired tools people have some downloads available on their website that include vacuum diagrams, installation instructions, etc that you can look at before you buy.
__________________
Richard Wooldridge
'01 ML320
'82 300D 4.3L V6/T700R4 conversion
'82 380SL, '86 560SL engine/trans. installed
'79 450SL, digital servo update
'75 280C
Reply With Quote
  #7  
Old 02-20-2006, 09:56 PM
1979300SD 24 years
 
Join Date: Jan 2006
Location: Bourbonnais, Illinois
Posts: 16
servo repair

There is a guy in Oak Ridge, Tenn. George Murphy he wrote the best article in The Star on servo repair. He currently repairs and guaranties for a year. After that 95$ to rerepair his work if something goes wrong 865-482-9175 or perfanalysis@comcast.net. The servo is a bugger, but most people do not maintain their coolant -every two years power flush and replace coolant -otherwise junk wrecks the servo. I have a 300SD and have driven 24 years.
Reply With Quote
  #8  
Old 02-21-2006, 09:25 PM
Registered User
 
Join Date: Nov 2004
Posts: 20
Although I don't know it for sure, I suspect the unit in my car was done by Performance Analysis. I tried the number, but George is on vacation right now.

In the meantime, I still want to go through the diagnostic procedure and pinpoint the fault, and one thing that has been tripping me up is the portion that says to apply +12V to one terminal, and -12V to another to check the operation of the solenoid. I read this as a total potential of 24 Volts, and that just doesn't sound right. Do they mean +12V and ground - that would make a lot more sense to me.

Once I sort out how much voltage to apply, I expect I'll know more about the health of my servo. But I don't want to fry my servo in the process of testing it.
Reply With Quote
  #9  
Old 02-21-2006, 09:50 PM
Registered User
 
Join Date: Dec 2000
Location: Battle Ground, WA
Posts: 576
Yes, they mean +12 & Ground return...

What they could have said is the + side of the 12v source and the - side of the 12v source. By the way, I notice that the guarantee on the unwired tools unit is 5 yrs.
__________________
Richard Wooldridge
'01 ML320
'82 300D 4.3L V6/T700R4 conversion
'82 380SL, '86 560SL engine/trans. installed
'79 450SL, digital servo update
'75 280C
Reply With Quote
  #10  
Old 03-04-2006, 01:39 PM
Registered User
 
Join Date: Nov 2004
Posts: 20
Unhappy

OK, I have finally gotten back to it. Putting power to the terminals resulted in smooth sound of the motor, and an even change in resistance between terminals 1 and 2. So I proceeded to take the upper part of the servo apart, per instructions in the Mercedes Technical Book published by the MBCA. It was clean inside, with only assembly grease evident - no coolant. The shaft of the water valve seemed to move very freely - too freely in fact. So at this moment, I suspect it as the cause of the fault, and I will be in touch with Performance Analysis regarding a remedy.

Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 04:28 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2024 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page