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Old 03-11-2013, 01:45 PM
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Join Date: Aug 2005
Location: Palmdale/Ventura, CA
Posts: 813
Climate Control Servo removal Auto Temp II AC 1980 300D

I know this topic is off-topic to the purest who wants their car original.
But I finally dove in and removed the under hood servo, the amplifier behind the glove box, and disconnected the vacuum line harness going to the servo.

Behind the panel in the dash disconnected the 4 vacuum operated electrical switches and the 4 electrically operated vacuum switches.

My goal:

1. Control the fan manually, Off 1 2 3 speeds.
2. Activate heat (open hot water line, turn on pump, activate needed vacuum pods).
3. Activate AC (turn on compressor, activate vacuum pods).

My original design was to create three fused circuits with three electrical switches.
The fan was simple enough, control the fan manually.
The heat and AC involve electricity and vacuum, so these each needed
a electrically controlled vacuum switch that would control the required vent pods.

The original idea was going to completely bypass the center console panel and interact with the various fan, heating , cooling parts directly.
Like any cheap manually operated car.

It turned out that I was able to use the original panel to control my vacuum pods and fan speed and AC compressor.
So it is much cleaner then I had thought it would be.

Where it is now:
After starting the car I need a switch to cut all power to the cabin fan/blower.
If I turn this switch on the fan blows on low (even in the off position).
Lo is the same speed. Hi and bi-level move to a higher speed.
So I basically have a two speed fan.

Testing the backside of the climate control panel I determined which buttons activate which vacuum lines and connected the pods directly to get
floor on bi-level and dash air on Lo and Hi.
Defrost override still works (it always bypassed amp and servo).

I took my power for the fan from the blue wire on the back of the climate control panel.

Using the AC Compressor switch I simply ran 12v to it and ran that to the compressor.

My center vents were already clamped open permanently so I can control
vent air by simply closing or opening dash vents.

So far I have set the stage to now connect or disconnect pods as needed to
get the airflow I want.

My next goal is to find a 12 volt water valve to replace the manual one
where the servo was removed. Right now I have the manually operated valve
that is well documented on this forum for doing wintertime heat.

I have owned this car since 1984 (second owner) and have always kept it factory original and working 100 percent. Two Auto Temp II servos (this one is the aluminum one), two amplifiers, two AC compressors. Recently replaced the climate control panel after the old one leaked vacuum.

I owned (and sold) the very rare Climate Control test equipment shown in the Mercedes Benz service manual for diagnosing the climate control system.
Still have the original MB manuals on the complete climate control system.
And have the Chrysler version provided by the Imperial group.

I would rather purchase a 1981 or newer MB without the ACC Servo than
own one of these. Seriously.

After owning this car 29 years and getting too old for some of this my
changing out the factory system is a last ditch effort before most likely
getting rid of this car.

Where I live it gets below 40 in the winter, and over 100 in the summer.
We like our cars to heat and cool when needed.
For years I had thought about what it would take to simplify the system
to provide basic comfort and finally tried it.
The other $500 option was the replacement system for the servo
but it still relied on so much of the original design I just did not want another
short term solution.

Flame suit on, sure you folks think I have broken some cardinal rule or am too lazy.
But this was a lot of work and it just might end up being a solution.
80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250
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Old 03-11-2013, 04:29 PM
Zacharias's Avatar
Not so amused
Join Date: Apr 2010
Location: West Quebec
Posts: 4,025
I am not sure why anyone would criticize you. On top of the fact that it's your car and you can do as you please, you certainly seem to have paid your due diligence dues over the years with both your equipment purchases and your running repairs.

I, for one, view purity as a relative virtue, both in women and in automotive repairs.

You seem to have a handle on what you are doing. In the past, I have seen people snapped at for whining about not being able to make the system work with a manual control valve they pulled off a Toyota and a long piece of string. Hardly the case with what you have written so far.

I owned a '79 300sd for eight years and only had to do two minor repairs on the Type II, and never the servo. This lulled me into a false sense of confidence in the system. Having bought a 1980 300td many years later has taken care of that.

If you do come up with a replicable solution that at least provides basic airflow and temperature controls at less hassle than doing a complete manual control system (240d) transplant, I will be standing at the head of the line of those who wish to copy it.

I do encourage you to take photographs where practical, if you are able, and if you want to share this later.

2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22
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Old 03-11-2013, 04:53 PM
Registered User
Join Date: Jul 2008
Posts: 3,740
Hey I am on board too! I would love to find a way to have the original purpose of the acc II work with out having to buy the 750$ kit which doesn't use the fresh air flap. My system was working great...I have a new servo/amp/sensor tube/unfroze aux pump and working vac pods....but last night I got in the car and couldn't get the system to work...even the deforst didn't I am lost at where to look now....but I like the system....just wish there was a cheap way to upgrade the system.,
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Old 03-11-2013, 09:37 PM
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Join Date: Aug 2011
Location: Carolina
Posts: 1,302
Originally Posted by rhodes2010 View Post
My next goal is to find a 12 volt water valve to replace the manual one
Electric Solenoid Valve 5 8" Barbs Water 12 Volt 12VDC | eBay

works like a champ!
Current fleet
1992 300D "IceBerg"
1984 300D "Blues Mobile"

1978 300CD "El Toro" Gone on to be born again
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Old 03-12-2013, 12:19 AM
shadetree77's Avatar
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Join Date: Jul 2003
Location: Tennessee
Posts: 430
@OP: i'm stuck with the autotemp II on my '79 SD as well. i found a working servo and amp at the wrecking yard. so far (3 months) it's been working like it's supposed to. i actually went ahead and coated the plastic portion of the servo in epoxy in hopes to prevent any cracking; only time will tell if it holds up. i'm still planning on doing a manual climate control swap once i source all the parts.
1983 300SD (daily driver)
1991 420SEL (work in progress)
1979 300SD (future replacement for 83 SD)

1983 300SD (totalled)
1986 420SEL
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Old 03-12-2013, 12:38 AM
79Mercy's Avatar
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Join Date: Mar 2008
Location: Florida
Posts: 4,128
I inherited my 1979 280CE from my grandparents, its been in the family since 1990-1991, looking through the old records it looks like between 1990-2013 it has had 3 servos installed, two vacuum pods, and one cracked vacuum line near the battery tray replaced in that time span.

As for now i plan to keep my original system to keep it original, i do not ever plan to sell this car.
1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles
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Old 03-16-2013, 11:53 PM
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Join Date: Aug 2005
Location: Palmdale/Ventura, CA
Posts: 813
PHILLYTWOTANK !! That valve is excellent. But it is rated for 195 degrees F - is that a problem ??

The vacuum ones I mention below are rated to 270 F and are automotive applications.

Searching vacuum operated water valves I found several that are cheap
like that electric one.
But So far the two I looked at are open all the time and need to be vacuum operated to close.

I am looking for a water valve that is closed all the time, and open when activated/needed.

A part number from Everco / Murray / 4 seasons
74612 or 74802 or 74803
which I got from cross ref of D4AZ-18495-A .

You all can look these up as possible valves but they are all open by default.

I investigated vacuum operated as it seems to be in line with the Mercedes
method of using vacuum for things and thought that would be cool.
I worked out the simplest single switch for heat that I could.
One 12 volt switch to activate the water valve and electric water pump.
That is all it will do.

The local auto parts store folks are not too familiar with these valves so I am left asking to see one and having to open each box.

I could not find a reference guide on line that explained each valves operation. That would have helped.
Attached Thumbnails
Climate Control Servo removal Auto Temp II AC 1980 300D-water-valve.jpg   Climate Control Servo removal Auto Temp II AC 1980 300D-water-valve-electric.jpg  
80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250
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