Modified AC Servo Question

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I installed one in my '80 300SD. Works fine.

The servo and amplifier are gone and a vacuum powered hot water valve and four electric vacuum valves are substituted. A circuit board inside an enclosure is the "brains" and is mounted under the hood.

If you install one be sure to ground all its components - even if you have to add a few wires.

Instructions (last year) were a bit evolutionary and hopefully have been rewritten for better communication.

Thanks a lot T.G.. How long did it take you to install, and do you think the average weekend MB mechanic can put it in?

Larry

They claim this retrofit is a two hour job - probably for someone who has done one, not for a first timer. That's not to say the job is difficult or physically hard. it's not, but the items to be worked on are unfamiliar.

The kit that was sent to me was a return, complete with greasy finger prints on its instructions. That's due to Performance Products, not Unwired Tools. Its heater hoses didn't fit so I had to substitute, Unwired wasn't aware of that until I mentioned it to them; hopefully that's now corrected.

I suggest you think about the location(s) of the electric vacuum valves and the controller; then block out an afternoon for this retrofit - and have access to another car in case you need to buy a substitute part.

The job has these phases:

Remove the glove box to access the amplifier. Remove the amplifier and add some jumper wires to that harness. Reinstall glove box.

Remove the servo ( I also removed the weeping aux. water pump.) Install the hot water valve in the heater's "hot" line and a piece of pipe in the heater's return line. (The instructions tell one to do this heavier work AFTER the vacuum lines etc. which is, IMHO, backward as one then disturbs the vacuum lines etc. while working on this heavier plumbing.

Then one installs the electric vacuum valves at a logical location on the fender or fire wall (be sure to run a ground wire from this bracket to the car's body). There are four valves, one for the hot water valve, one for the fresh/recirculating air, one for the upper vents and one for floor vents. The directions as to what connects to what are clear; YOUR decision is whether to retain and plug into the old servo vacuum harness or cut the old vacuum lines (one by one to avoid confusion). This decision and your location of the paperback book size control box, ties into how you want the end result to look - neatly tied up or a kludge of tubes and wires etc. . Neat takes time.

The electrical wiring is relatively easy (but don't tug on the wires as some may pull out of their connectors).

Finally, the control box is plugged in. Drive the car and then, at operating temp., calibrate the controller (one tiny adjustment screw).

There's no change to the original console / dashboard appearance, all the changes are under the hood. I especially like this feature.

The kit omits the OEM cold engine lock out feature. I restored it by salvaging that vacuum / temperature switch from the very bottom of the servo and attaching it to a flat brass plate that I soldered onto the copper pipe in the heater's return line. The vacuum switch is cut into the green / white (fresh-recirc) vacuum line. It works just like OEM, even without the electric aux water pump.

The kit includes a five year warranty.

I like my old car but hated that lousy servo - this kit solves my conflict!

Hope this answers your question.

I'll say: excellent answer. Thanks, I'm sure that many other people will find it useful too as they start replacing those out-dated contraptions.

Doesn't sound too difficult I was just wondering, though; did you have to drill holes to attach the box to the firewall?

Larry

BTW. 5 years doesn't seem like a very good warrantee. Should be at least 10 years, imo.

Larry

Actually, the bracket for the electric vacuum valves was screwed onto the top if the 116's right fender and a plastic food container wrapped over the valves and their plastic tubes etc. and the controller was tied onto the plastic vacuum lines that were looped and secured onto the fire wall. Those nylon cinch-ties are worth their weight in gold! The 116's fire wall has most of the vacuum lines and electric wiring and the controller.

The unwired tools site has pictures of an excellent installation whereby an owner cut down a plastic box to cover the valves etc.

Five years is a long warranty on electronic parts, IMHO. The controller is the only unique item that really needs a warranty, the other stuff is common parts. But the $$ value is that someone figured out a way to emulate the old system with modern parts.

And it does work.

5 years isn't a good warranty on a car part? Good grief! It's the best I've ever heard of and seems especially good for a warranty on something intended to replace an OEM electrical/vacuum/water component on a 25 year old car. What kind of warranty would you get from the stealership on even a simple electrical part?

BTW, if you don't want to go the conversion route, there is another alternative. Performance Analysis Co, in TN offers rebuilt servos that use aluminum housings rather than the original plastic, which was the cause of one of the main failure modes. I think they cost $600 with a

1 yr warranty. But after that, if it fails they will fix/replace for $100.

I went that route. My experience has been that even the OEM ones lasted for several years and if I can get it fixed after that for $100, it was a good deal.

Received the new Performanceproducts4benz.com catalog (49M) today and read that the retrofit digital servo is now priced at $499!

And the text on the inside front cover says "Installs in less than 2 minutes"

Wish I was smart enough to install it in 2 MINUTES!