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Registered
1989 560SL
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152 Posts
Discussion Starter #1
If the servo valve is the source of battery drain due to being stuck; is there a way to get it working again without taking it apart?

The tutorials for rebuilding a servo valve are daunting to me. Is there a way to flush or free up the internals in place?
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
Joined
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7,150 Posts
If the servo valve is the source of battery drain due to being stuck; is there a way to get it working again without taking it apart?

The tutorials for rebuilding a servo valve are daunting to me. Is there a way to flush or free up the internals in place?
Not to my knowledge. I have seen valves torn down, and haev replaced on on a friend's car, but I have not torn one down personally.

BEst ditch it fo rth eUnwired Tools digital replacement... ScotinSoCal can give you advice and feedback on its performance.
 

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1980 450SL & 1988 560SL
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1,667 Posts
If your amp is bad the servo could be fine. The amp is what supplies the power to move the servo to it's requested position. Remove the servo cap and change the temp settings and listen and watch to see & hear it run. The temp guage in the dash, the temp control work together to bias the amp to move the servo to the correct position. The servo turns the hot water on and off and routes the vacuum to the correct pods.
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
Joined
·
7,150 Posts
If your amp is bad the servo could be fine. The amp is what supplies the power to move the servo to it's requested position. Remove the servo cap and change the temp settings and listen and watch to see & hear it run. The temp guage in the dash, the temp control work together to bias the amp to move the servo to the correct position. The servo turns the hot water on and off and routes the vacuum to the correct pods.
He is chasing a battery drain, and I suggested the servo may be locked up and not parking... Will the servo not park, regardless of the amp, when the ignition is shut off?

Incidentally, a locked servo has been reported to kill the amp, like shorting a monovalve will likely kill a climate control panel on the later models ...
 

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Registered
1989 560SL
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152 Posts
Discussion Starter #5
Servo Valve

Okay,

I am attaching a picture of the servo valve with the cover off. What should move or rotate when you ask for heat with the cabin controller. I can't see anything that looks like it would move without further dis-assembly. Motor noise makes it hard to hear if the servo is moving and the aux pump is not running either.

I do have current with the key off and the negative disconnected. I think it reads 0.4 on the 10 amp scale so there is a good draw but I haven't checked fuses yet.

Does this draw indicate that the amp is okay?

I plan to sell this car so maybe I will be best off to just tell the next guy that the heater doesn't work Maybe someone in Florida will buy it.

I hate to give up on anything though. But money can become a problem pretty quickly with these cars.
 

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Registered
1989 560SL
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152 Posts
Discussion Starter #6
I disconnected the electrical from the servo valve and the current drain stopped. One problem solved but now what to do about the servo.....
 

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Registered
1980 450SL & 1988 560SL
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1,667 Posts
The little pot has an arrow in the middle and the pot turns with the servo. If that is the servo you got from me, it was a working unit. I don't know about the parking issue with a bad amp. I hate this system of heat/AC.
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
Joined
·
7,150 Posts
I disconnected the electrical from the servo valve and the current drain stopped. One problem solved but now what to do about the servo.....
If you had a current drain with the ignition off, the servo is trying to park and can't. This usually means down deeper than what you have exposed, the water valve has corroded and locked up or at least partially locked the shaft, and the valve shaft can't can't turn to put the electrical switches in the park or "no current drain" position. If the valve can't turn, the proper vacuum elements can't get vacuum, and the appropriate doors will not open to direct air as desired. Also, the water cannot be regulated for the heating, nor can the fan speed be controlled as designed. Also, since the servo can't park, it is constantly drawing current, trying to turn the valve shaft(and all the other connected electrical switches and vacuum switches).

I am going to try and find the link to the chrysler imperial manual (from which our systems originated) and post here... Stand by...

Edit for link: http://www.imperialclub.com/Repair/Lit/Master/281/index.htm

Obviously, not everything in this attached document is applicable, but you will recognize what is and isn't. I have also attached the link for several articles regarding the Chrysler system. You may find other references that apply.

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

Enjoy reading, and good luck.
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
Joined
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7,150 Posts
There used to be a link from the chrysler page, to a guys "imperial" page, with cool pics of a servo in various stages of disassembly. The quality of the pics left a little to be desired, but were clear enough to get the point across. Page 13 of the manual I posted (in the first link of my last post) shows the wiring diagram. That is the best diagram I have seen of the "system"...

An electrical engineer friend of mine and I were working on a replacement (similar to unwired tools product). Then I saw the UT ad for the servo replacement, and we shelved the project.
 

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Registered
1989 560SL
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152 Posts
Discussion Starter #10
Don't worry about it. I will look at it a little closer if the weather holds and I can get one car out and this car into the garage. My problem may be the amp. I'm not sure how to test it though.

Those little hoses on the top of the servo are kinda loose also if they have to transmit vacuum and hold it.
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
Joined
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7,150 Posts
Don't worry about it. I will look at it a little closer if the weather holds and I can get one car out and this car into the garage. My problem may be the amp. I'm not sure how to test it though.

Those little hoses on the top of the servo are kinda loose also if they have to transmit vacuum and hold it.
I don't think the amp has anything to do with the servo parking, but I could be wrong (reference wiring diagram). The amp has a direct battery feed to the servo to park, when the switch is off, or the pushbutton is pressed to off. The fact you have the drain tells me the servo has received the command to park, but physically can't.

Anyways, good luck with your project. At least you found your vampire...

Edit... Obviously, the amp does have something to do with the servo parking, but it is a separate circuit, adn the fact that the servo is draining, implies the command has been received to park. All power to the servo comes from teh amp, until the servo parks, then the separate circuit is broken, or cut off... I think! Its just like the wipers parking... once the servo gets to the park position, the current path is broken and the re is no more electrical drain.
 
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