Need help from the SD crowd

[anhydrous7]

I have a 1982 300SD. I have been doing troubleshooting on the ACC system. I isolated the problem down to the ACC itself. I purchased a rebuilt unit from Beckmann Technologies in North Carolina. My car did not come with an owner's manual. Does/Can anyone scan or copy the pertinent areas for the ACC operation. I am not sure how the air flow is suppose to work with the different buttons selected. When I installed the rebuilt ACC, it worked for three days the way I thought it was supposed to function. Now, no matter what button is selected, I always get some amount of air flow from the defroster vents close to the front windshield. I thought possibly the vacuum actuator was the culprit, but when I roll the temp to the cold side the vacuum actuator cycles and I get air blowing from the center vents and no air coming out of the defroster vents (obviously not set in defrost mode on ACC).
That is another question. My 300SD has the slides for the center and the two side dash vents that will close off airflow from/to the dash vents. I assume that these center vents are for air conditioning and vent use only. Is this correct? I believe this is unique to the 300SD. Our 300D brethren do not have these slides to close off the dash vents.

Any help would be appreciated. I am also trying to contact Beckmann Technologies, but can not get anyone to answer the phone. I believe they got hit pretty hard early last weak by the ice storm that passed through that way.

Regards,
Rob

Spoke to the folks at Beckmann. They were pretty quick to diagnose it as a vacuum actuator problem. I am not saying that it can't be it, but was wondering what other experienced SD owners think. In doing searches it sounds like this may be the actuator that requires the dash to be romoved to gain access. I have the CD manual and have been trying to find pertinent info on troubleshooting.
What has me puzzled is that I can rotate the temp controler and the air flow will switch from defrost to dash vents. Only in the hot mode will air come out ouf the defrost vents. Possibly there are two vacuum actuators involved here?

Your help would be appreciated.

[sixto]

In the first disk of the CD manual, there's a file called ACC83-85.pdf in the ETM folder. Towards the end of the file is a table that tells you what each ACC component should do given particular siwtch and sensor conditions. The file OM-22 in the OM folder will guide you through using the ACC. The manual is for 91 model year V8s, but most of it is the same as in your car. There is a specific section for testing the AC vacuum system.

The peculiar thing about many MB AC systems is that you can't get hot air out of the center vents. I don't understand the logic but that's how they are.

If we accept that that much of your system is working properly then the next suspect is the vacuum actuator for the footwell vents. The footwell actuator is the one behind the controls that moves a rod to the left and right as viewed from the driver seat. You don't have to take the dash itself off to get to the footwell actuator, but a good amount of the console has to come apart.

FWIW, there are 6 vacuum actuators. Two are above the glove compartment and control the recirculated/fresh air flaps. One is high in the dash and controls the defrost vent. One is behind the controls with a rod that goes left-right to control the footwell flaps. One is behind behind the controls with a rod that goes front-back (relative to the direction of travel of the car) to control the dash vents. The last one is by the accelerator pedal with a rod that goes up-down to control the diverter flap (I think that's what it's called). The default (no vacuum) position of the defrost flap is open, all the others are closed until vacuum is applied.

Sixto
91 300SE
87 300SDL
83 300SD

[anhydrous7]

Sixto,

Thanks for this insight. My system may be working somewhat as designed. It sounds like when you are in positions a and b, there should be at least a slight amount of air exiting the defroster vents. I also found a statment in the CD text that said you should leave the slide adjusters slightly open for the most efficient operation of the system. They also made a statement that when you start out in a or b and switch to c or d, the 33° C coolant temperature cut out is over-ridden.

What you said about the footwell vent vacuum actuator merits further investigation. I will investigate that next.

Thanks for your input. I will report back on my findings.