Has anyone ever tried to fix/rebuild the climate control servo?
 

Car is the 1979 300SD w116. Mine isn't working now. If I remove it and spray wd-40 in the small holes and put it back in it will work. I did that like 2 months ago, and it worked until recently it wouldn't work intermittently. I know this can be rebuilt because I have seen them for sale but is it something that I could do or is it too sophisticated? Also, how do I check the amplifier that is behind the glovebox?
Thanks
David

I've always heard that they seize internally. Never even tried to disassemble one. "Replace it" seems to be the order of the day, but you probably have nothing to lose by taking it apart.

Gilly

To check the amp , remove the glove box (123's anyway) and then remove the amp. It's a black box with mesh openings about the size of a deck of cards.Open the amp up and check the soldered connections on the circuit board , if they look burnt the amp may be beyond hope. Mine were brown and I resoldered the entire board , it's worked fine since. Fix the servo first then the amp , I believe the servo (if it seizes) will fry the amp. Good luck.

Most of the servos that I have seen failed due to the plastic body cracking. I've got to think that internal corrosion may have something to do with this too. I've got one that is cracked in my pile and would love to give rebuilding it a shot but where does a guy get the aluminum body or just another good plastic body to use in the rebuild process?
I'm guessing that the rebuild shops have them built specially for their use but maybe someone knows of a source?

The thing is though, mine isn't cracked. I just don't think it's opening. When it would work I could turn off the car and hear it close. I know it did that when I had defrost on when the car was shut off. You would have to open the hood and stand by it but you could hear it run for about 15-20 seconds. That is why I am wondering if it may just be something simple on the inside that I will notice wrong right away.

I think there are 10 wires going into it. Do any of you guys know what color/wire should be getting what voltage; so I could maybe make sure it is getting the proper electricity?
Thanks
David

Testing
 

I don't know if you have ever looked at the troubleshooting doc on the CD for the servo but it has like 2 tests and that's it!
Really lame..

I just looked at all the wires, the vacuum tubing and the brass bars on the top and decided to stop there...;)

Now you've got me thinking to tear into it since my case is broken anyway and see if I can make heads or tails out of the thing.
I'll let you know what I find, if I can get a chance to get to it.

I want to tear mine apart but then I don't have a way to get to school. Chances are, when I get it aprt I will break something rendering it useless. I am thinking of maybe just bypassing the servo for now by just using a pice of pie to connect the hoses together. I just need to figure out which hose goes where.
I want to wait till after I subscribe to Thomaspin's site so I can see what his is alll about with the climate control.
Thanks
David

There is (or was) a tool available for easy testing of the servo. It consists of the electrical plug (like the one on the harness that connects to the servo-motor) and 4 wires. 2 of the wires are to power the servo-motor. The leads are long enough to reach a battery, either the car battery or a test battery. The servo-motor evidently runs on less than 12 volts, as there is a resistor to evidently step down the voltage, but I don't know the operating voltage or info on the resistors used. The other 2 wires you connect to an ohm meter to monitor the feedback resistance. Movement in the resistance indicates an operating unit.

Maybe someone has info on the parts needed to make the tool. Maybe I can try fishing up some info myself too.....

Gilly

Located the following site while looking for info on various aspects of our '64 Imperial. Lots of good info in the "servo" section including an internal layout diagram for their servo. Can't rember seeing a circuit diagram but it at least explains some of the internals for this somewhat mysterious part.


imperialclub.com/Repair/Lit/Master/281/index.htm

Where are the holes located that you sprayed the wd-40 down? I am almost tempted to do this, as long as it doesn't require too much disassymbly...

When I bought my '79 300D in August the servo was bypassed. The seller told me she did not want to spend the money so her indy shop suggested the bypass. They just connected the lines straight through under the servo - leaving the servo in place and connected. Problem with that is you have heat all the time and the climate control buttons cause some pretty neat reactions when you press them :D
I did not want to deal with the heat and also wanted some functionality so I had my indy install a rebuilt - all is well now. The rebuilts seem to run about $350 from most places.

I know that there is a rebuilt servo out there with an aluminum body that won't ever crack. The price on them is roughly a 1/4 of a new plastic one.

The holes are rectangular and the perfect size for the "straw" to fit into. It has to be out of the car to do this. They are abouot mid-way up on it. Also, you many want to spray carb cleaner first to clean up the inside if necessary. Or, just put a wanted ad in the parts discussion and see how much you can get one for. Are you sure it's your servo? It could be the push-button unit or the amp on the passenger side under the dash.
Thanks
David

That is so cool. I have been looking for something like that since I bought my car.

THat link is deserving of a sticky if ever I saw one.

Very Cool site! Like ACC for Dummies :p I actually understood some of it :)

A few years ago, I experimented with the servo on a friend's '79 300D. The AC was shot and he just wanted some kind of heat in the car so his son could drive to school in winter. The only thing working in the climate control was high defrost with no heating. The servo's coolant valve had seeped vapor into the cavity below the motor and turned it and the little gearbox into rusty junk. I removed the rusty machinery and made up a neat little cable operated cam and lever device to replace the servo motor assembly and operate the vacuum valve and fan control. Unfortunately, possibly due to the fried amplifier, my experiment failed. So I bypassed the servo's coolant valve and rigged the cable control to a manual Dodge Omni heater valve. Now my friend still has the high defroster fan, plus a way to add some heat.

Happy Motoring, Mark

Just so its a link that is clickable.

www.imperialclub.com/Repair/Lit/Master/281/index.htm


I bookmarked that. Somebody needs to archive the whole thing for posterity in case that site closes.

I just opened up my AC Servo, and am cleaning up and lubercating everything inside, and sealing the cracks in the plastic. My motor is running just fine, so I hope by doing this, it will work like new after I get everything put back together. :D

I almost had everything back together, then the little clip that connecets the rod to the plunger broke off. So I had to pull the servo out and take the whole unit apart. I had everything back together once again, and the clip came loose again, so this time I used the pliers to press it together and the top part broke off. I decided I could use some JB weld on the plunger to, and put the little rod into it, I am hoping it will hold together. Tomorrow I will put it all back together once again. Does anyone know where I can but just that little plunger the metal rod and the clip???

My conclusion is that tearing the AC Servo apart, and putting it back together is bad. I had everything working perfect for a short time, then the pressure knocked all the screws loose, and it leaks bad now. I am going to bypass the whole system with some kind of adjustable valve and copper pipe...

Mikemover posted this link in another thread.

( )

A digital solution to a vacume servo monstrosity.

For a measly $350 you can buy a rebuilt unit ;) Mine has been working great :) (i think there is a core deposit also)

True but a siezed servo usually fries the amp.............so even more money and how long will it last? its anyones guess. If your servo is cracked adn coolant got in and smoked it , then its not rebuilible and you get no core charge returned to you, as me how I know that.

Its a more reliable in not a slight bit more costly replacement option.

I year ago I would have hopped on it. If mine dies again soon, I still might.

We have recently put our '82 300SD back on the road for winter duty and just a few weeks ago our fan became stuck on high/Defrost only. I do hear the vacuum and the flap or vane or whatever moves insde the heater unit to direct airflow, but nothing changes. Am I to assume that my servo or amp is starting to go down?

Please help my eyes can't take the heat no more!! :eek:

You won't have an A/C Servo, they were used from 1977-1980...

Got it. It is 3 megs total. Anyone wants it emailed, yahoo and hotmail are now supporting these large transfers, just let me know. If it goes down, I will repost it.

Too much to read for me right now. Too tired. I tinkered with mine until I just bypassed it, maybe now I will have the drive to go back and figure it out.

By the way, that thing was printed in 1971. What the heck was MBZ thinking putting that beast of ancient technology into cars ten years later?

I discuss my simple bypass here:
http://www.peachparts.com/shopforum/diesel-discussion/110502-%242-servo-aux-pump-bypass-fix.html#post771037

Telecombrkr your problem may be a simple vacuum leak , have you been under the dash or hood lately ? I had the same problem when I was installing the stereo in my car , and I unknowingly knocked a vacuum hose off. The climate control vacuum source under the hood is in the brake master cylinder area.

Based on your symptoms...
 

The default function with a total loss of vacuum is defrost so based on your symptoms it may just be that a vacuum line got knocked off while you were working on it.

On the SDs you can access all the vacuum pod control valves by pulling the carpet on the passenger side kick panel. They are in a nice vertical row there and you can test each pod from that point wihtout having to take out the console like you do on the 123.

bump tht...

I've taken my 80TD's apart three times, with one replacement from the yards. WD-40 is a bad idea as it causes rubber to swell. WD-40 is a bad idea on all rubber and plastic. Use sythentic (ie...silicone) grease or lithium grease and may get better- mine did. Be sure to check that the lower plunger actually opens and closes. Be sure to check you have vaccumm to all the lines which enter the servo. It's really not complex inside- just delicate. Like a big very simple clock.

I believe Performance Products is selling a kit of modern components that replicates and replaces the servos. It's reliable and should never require periodic replacement such as the first-generation ACC servos do. The traditional servos can both seize internally OR crack on the outside. The "rebuilt" units with aluminum bodies aren't worth the money unless the internal mechanisms are new.

My suggestion and advice would be to investigate/purchase the Performance products solution. I remember it to be around $500-600 -- this is roughly half the cost of a new servo from MB.... and other than the aluminum-bodied "rebuilds" I believe that MB is the only company selling new units. And they've been playing around with the prices on them in recent years.

Cheers,
Gerry