ACC Amplifier

[jbrasile]

Hello everyone,

The ACC in the 78 450SEL started to act funny, either be too cold or too hot, no in between control.

Servo is aluminum, installed about 3 years ago and still functioning as it should and the amp was replaced at the same time even though the one that was in there was actually working. At that time I noticed it to be an aftermarked non VDO (Made in Mexico) unit and put the new Made Germany in.

Temp sensor hose has been repaired with the appropriate a/c foam tube.

I have 2 brand new amps I purchased at a local dealership fire sale 2 years ago and decided to give them a try.

Guess what.... after trying both of the genuine German items I settled for the good old Mexican part!!! From looking at it it seems to have an i/c in place of some diodes present in the original amp and it is working flawlessly!

Just goes to show you that sometimes our prejudice towards some non original non OEM parts can be unfounded. I have always noticed that after replacing the servo/amp combo in 2008 the ACC was always a little iffy, never quite right in its temp control. It is perfect now except that I still feel like there should be more air coming out of the dash vents.

There are two versions of ACC installed in 116's, one lets air "leak" to the windshield vents in all operating modes and the other does not. It is odd because when I bought my car it did that and every manual I have looked at says that my VIN should not have this feature. This "leak" is controlled by a dual function vacuum actuator which is located in a place almost impossible to access and of course mine has a leak. What I have done is block the vacuum line going to that actuator and locked the center flap in its open position. The draw back is that my center vents never close except when in Defrost mode and that affects correct temp control.

One of these days I will spend some more time analysing this situation to see if there is anything else I may have missed that's keeping me from having a full blast of air thru the dash vents. As time passes a manual a/c conversion becomes more and more tempting...

Tks,

Joe

[WGB]

Does this system suffer from teh same airbox flap issues of disintegrating foam as the HVAC system?

Bill

[jbrasile]

Bill,

It actually doesn't and because all the flaps are controlled by vacuum actuators they don't tend to "flop" around as older HVAC systems do.

Joe

[1980sdga]

You can't abandon your ACC!  How did you block the vent?

[jbrasile]

I don't want to abandon it.... but having had a manual system in the 74 280S there is no comparison...

My center vent does not have a manual closing feature as 79/80 cars do so I disconnected the actuator arm from the vent flap and simply pushed it all the way back, then I opened the flap and let the arm simply sit touching the open flap. The actuator vacuum line is plugged too this part of the system is basically deactivated.

Tks

Joe

[thysonsacclaim]

Totally with you on the bias towards parts.

While there is some true quality differences in some things, sometimes the alternative is just as good or better.

[1980sdga]

Joe, Where can I find a rebuilt amp? I have 2 which seem to be intermittent   

Both have cold solder joints that I've repeatedly repaired but they don't seem to stay fixed.  Seems I just can't get solder to stick to the legs on the big grey resistors. The resistors also look a little dodgy from what appears to be overheating. I have a new aluminum servo but I'm thinking that my old creaky servo did some damage to the amps.

I've been trying to contact George Murphy.

[jbrasile]

Jon,

George should have them new.

Here is his contact info again:

865-482-9175

email: perfanalysis@comcast.net

If you still can't get in touch with him, I can supply the rebuild amp for $195.00 + shipping

Let me know.

Tks,

Joe

[1980sdga]

Thanks Joe. Mine has been working fine for a few days but I'm waiting for it to crap out again 

Strange thing, this AM with the car off, after sitting all night the amp was warm. I did leave one of the buttons pressed so I guess it's still "alive" with the ignition off. I thought it always parked?

About you not getting enough air through the vents. I think that with your fresh air vent staying on recirculate you are losing some airflow. Once my fresh air vent opens to the 20/80 AC position I get a good deal more air out of the vents. It's almost like another blower speed.  Maybe since the opening is bigger with the vent flap open? With mine on "hi" and the compressor "on" it blows pretty hard and cools OK.

Too bad you have to take the footwell panels off to get to the element.

[jbrasile]

Jon,

That's odd your amp was warm after sitting overnight. I suppose leaving the Auto-Lo button may have send vacuum to the servo and so the amp was either trying to park it or trying to control a non operating system...

Interesting point about air flow....I will try and re-activate the re-circ flap and see what happens. I do suspect however that since the center flap and defrost vacuum elements have leaks, and I have taken them out of the control chain, that the defrost flap in the a/c box is only partially closed not allowing a full flow of air to the dash vents. That will be remedied soon... getting them changed without removing the dash I am sure will be an exercise in patience and I will have to develop new joints in my hands and arms, hehehe.....

Tks,

Joe

[1980sdga]

It may have just been my imagination.

http://www.youtube.com/watch?v=-bqjjF6yuXA

That's going to be fun changing that pod.  Isn't it double acting?

Once done you'll be glad you did it. Well worth the work! Mine seems to be working well and it's kind of cool the way it automatically switches from center vents to the defrost/legflaps. I smoke and I'm amazed at how well it keeps smoke out of the cabin.  No cupholders anywhere but ashtrays galore!

I'm looking forward to my first winter in one of these cars   

[1980sdga]

My ACC went out again today    It's gotta be the amp...

[1980sdga]

Another update...

I got in touch with George Murphy and should soon have a rebuilt amp on the way 

I decided on a rebuilt because maybe it has more robust parts and better QC.  Not sure if this is rational or not 

[pwiebwal]

Those resistors are probably getting hot enough to melt the solder. There is something else going on there.

[1980sdga]

I got my rebuilt amp in and it's similar to the one Joe describes. It has what looks like an IC in place of 2 diodes that were in the center of the circuit board. The big grey resistors have also been changed to a different type and the solder has been re-flowed on the back.

It's warm but no where near as hot as the old ones. Maybe the resistors were burned up causing it to overheat? Or the old crusty resistors may have been preventing the servo from parking?

The servo also sounds a lot "stronger" now, if that makes sense.

Hope you don't mind the thread hijack Joe.