AC - Evil Servo question - PeachParts Mercedes-Benz Forum

Maexle · #1 03-05-2013, 12:06 PM

I did now a lot of research on this matter, and for know i think am going to cheaper way, by bypassing the Evil AC Servo thing.

Has anyone accomplished this bypass :

early W123 servo bypass described/pics

and got the AC working ?

vstech · #2 03-05-2013, 12:13 PM

I've seen some cars where somebody uses a switch to turn on and off the compressor...

Maexle · #3 03-05-2013, 12:19 PM

Quote:

Originally Posted by vstech

I've seen some cars where somebody uses a switch to turn on and off the compressor...

I would be just fine with that.....

So, is it fact that, without that stupid servo, a working compressor and amp the AC get to work ?

cooljjay · #4 03-05-2013, 02:08 PM

Is your system charged? Before attempting to bypass the servo I would confirm your AC system is charged with freon or converted to r134. You have to also realize the servo and amp control all the vacuum flaps under the dash. The link added shows the bypass to get the heat to work and to get the heat to turn off. My AC system has pressure in it and the compressor engages but i have yet to top it off so I can't go into bypass. I would suggest that you pull the auxiliary water pump, free it up. Pop the glove box liner, replace the foam sampler tube and then replace the amp. If you have a vacuum leaks your servo will also not work correctly. Unless the servo is leaking chances are it is fine.

Maexle · #5 03-05-2013, 02:46 PM

Quote:

Originally Posted by cooljjay

Is your system charged? Before attempting to bypass the servo I would confirm your AC system is charged with freon or converted to r134. You have to also realize the servo and amp control all the vacuum flaps under the dash. The link added shows the bypass to get the heat to work and to get the heat to turn off. My AC system has pressure in it and the compressor engages but i have yet to top it off so I can't go into bypass. I would suggest that you pull the auxiliary water pump, free it up. Pop the glove box liner, replace the foam sampler tube and then replace the amp. If you have a vacuum leaks your servo will also not work correctly. Unless the servo is leaking chances are it is fine.

The servo IS leaking......

Maexle · #6 03-05-2013, 02:50 PM

Here some more background info:

1978 300D,
door power locks don't work,
heat / blower works only when on defrost (top position, i have the vertical climate control unit),
car won't turn off when on defrost,
No AC

cooljjay · #7 03-05-2013, 03:22 PM

Sounds like you have multiple problems. First I would fix the leaking servo, bypassing it won't make the ccu work any better then what it does. If you don't fix the leak, chances are you'll over heat the car and kill the engine because of the coolant leak. It also sounds like you may need to rebuild your vacuum pump, may not be enough vacuum pressure to control everything. You probably have leaking actuators in the doors, why the locks don't work. You can bypass them for now, they are not necessary for the car to run.

Phillytwotank · #8 03-05-2013, 04:16 PM

multiple vacuum related problems definitely points towards some major vacuum leak or weak pump.

agreed that you should address the servo water leak problem first. Benz there done that myself. My servo had small leaks for a while until one day when it practically exploded and dumped a whole bunch of coolant quickly. You don't want that to happen.

Then you can address the vacuum problems. By a mityvac and learn to love it.

as for the servo.. there are many options to restore partial or full functionality to the HVAC system.

I do believe that,servo aside, the ACCI design is pretty robust. It may require much less effort than you think to get everything up and running again.

Maexle · #9 03-05-2013, 05:40 PM

So, to rebuild that "evil" servo thing is something one with common sense and mechanical experience (and some electrical) can accomplish ??

Is there a DIY about this topics somewhere?
How to fix the cracked housing ?

cooljjay · #10 03-05-2013, 07:21 PM

I would warn against trying to fix the servo, I attempted this and it didn't work out to well. I was lucky and found a good one on eBay really cheap, if that didn't work I wouldn't have any heat. You can do the bypass you linked to and you won't have to worry about the cracked tank nor not having heat. The mono valve is built into the servo and this bypass will eliminate it....you will just have to manually operate it. There are also threads that show you how to put a coupler in for the hot water return and a simple PVC valve for the hot water feed. In the winter you simple open the hood and feed the hot water into the heater core and manually....then when it gets to hot open the hood and turn the feed off.

There are a LOT of threads out there on the evil servo just Google Mercedes 300d ccu

Maexle · #11 03-05-2013, 07:38 PM

Quote:

Originally Posted by cooljjay

I would warn against trying to fix the servo, I attempted this and it didn't work out to well. I was lucky and found a good one on eBay really cheap, if that didn't work I wouldn't have any heat. You can do the bypass you linked to and you won't have to worry about the cracked tank nor not having heat. The mono valve is built into the servo and this bypass will eliminate it....you will just have to manually operate it. There are also threads that show you how to put a coupler in for the hot water return and a simple PVC valve for the hot water feed. In the winter you simple open the hood and feed the hot water into the heater core and manually....then when it gets to hot open the hood and turn the feed off.

There are a LOT of threads out there on the evil servo just Google Mercedes 300d ccu

Are you serious? This means you actually have to pop the hood and adjust it ??? Well , before i go down this road, i heat up a stone over night and sit on it while i am driving..... just kidding....but seriously, is there no other (kind of) easy and not too expensive way to get the heat and AC going ? On / off and cold / warm would be good enough ??

cooljjay · #12 03-05-2013, 08:20 PM

Quote:

Originally Posted by Maexle

but seriously, is there no other (kind of) easy and not too expensive way to get the heat and AC going ?

Hold on let me think...um NO..whew that was hard

To get your AC going again, will cost 1000$-1500$ to get going again. To get your heat going add another 1000$....its a PITA no matter which way you go....even if yo get it going again there isn't a guaranteed period it will work....mine was working excellent besides the AC and when I came back from California I couldn't get any heat....mind you I tested and went through the whole system. You can always buy this kit, it will work but the fresh air vent won't work. Have you looked at the mess of vacuum lines next to the battery tray? Usually they will rot away with the battery try....best bet is to do ALOT of reading on it and dig in....famous last quote "ain't no such thing as a cheap Mercedes"

MB 300D 300SD 300TD 380SL 380SLC 450SE 450SEL 450SL 450SLC Climate Control Servo | eBay

shadetree77 · #13 03-05-2013, 08:28 PM

there are options with a manual pull handle in the cab or a homemade vacuum setup for the heat.

cooljjay · #14 03-05-2013, 08:37 PM

Quote:

Originally Posted by shadetree77

there are options with a manual pull handle in the cab or a homemade vacuum setup for the heat.

Yep there are a number of band aids but I think the OP just wants to push a button and get heat. You can get the hot water to the heater core but getting it to blow out the right vents or at all is the trick....

colincoon · #15 03-05-2013, 09:46 PM

I fixed my servo. Read my thread here and take notes.
Verify everything else works, then invest in an aluminium body servo. Mine still works just fine after all of this.