Here's the valve in place:



Still needs tidying up if it works.

I'm going to try keeping the aux pump. It works with power applied but a PO butched the wiring. Operation is pretty simple consisting of a thermostatic switch that completes the circuit when temps are below 79F so it shouldn't be that hard figuring it out. I'm also going to put an in-line fuse at the pump in case something goes awry...

It's outlined on page 16 here:

https://s3.amazonaws.com/sspublicweb/mercedes/Mercedes+116+Climate+Control+Service+Manual.pdf

I'm using the semiservo to control the blower speed only. No vacuum switching at the servo! My sensor chain is intact so it chooses the blower speed based on the difference between ambient temp and thumbwheel set point. I may see if I can simplify the servo vacuum switching so the water valve will only be open when the servo swings to one of the "hot" settings but since the valve is normally open it may be tough. I am trying to simplify...

If someone wanted to go further with this and not use the servo or sensor chain at all you could look at pages 20-27 and just jump wires across the plug that goes on the servo. There are 5 possible speeds so maybe you could pick one and jump the circuit.

I'm lucky that we're having record cold temps for April so I can do some testing on the road...

__________________
My occupational hazard bein'
my occupation's just not around...
1980 300SD
1980 300SD

Orphaned gear:



I tested the water valve and all seems to be well. Heat with BI LEVEL and DEFROST and off in the other positions! It's A LOT of heat but when the thumbwheel is set close to the in car temp the blower slows down.

The way the original plumbing works is pretty weird:



With the valve fully open all 4 nipples are connected. With the valve closed it shuts off one nipple and the other 3 are connected. There is some kind of bypass flapper valve that does something as well. I'm guessing that it allows the aux. pump to return water to the engine even with the valve closed.

Here's the new and improved setup:



I think I have less than $20 invested...

I would REALLY like to know if the UT servo replacement kit uses a variable position valve or a simple on/off deal. I've heard it uses a Volvo part...

__________________
My occupational hazard bein'
my occupation's just not around...
1980 300SD
1980 300SD

I feel so alone with my AWESOMEMOBILE.

Anyway...

The friggin' vacuum part of the servo has been sort of a mystery to me so I decided to attempt to figure it out.

This required a glowing crystal, a majik box and some runes written on the back flap of a German transmission service manual:



It wasn't a complete success because I'm still need 3 of Smokey Yunicks toenail clippings to place in the box, but it worked OK for my needs.

I discovered that by hooking a vacuum source to #6 and the heater valve to #5:



that the heater valve would remain closed until the servo turned to about the last 1/4 of the heat side

I did some testing with it everything mocked up in the car and used a vacuum gauge to tell when the valve was open or closed and it looked pretty promising.



Still need to tidy up a bit before road testing begins...

__________________
My occupational hazard bein'
my occupation's just not around...
1980 300SD
1980 300SD

I'm going space age. It's the 80's after all...

Arduino deal running a valve:

MVI 0135 - YouTube

Little computer runs programs and tells stuff what to do. It's just a program that swings the servo back and forth and I fooled with the timing/degrees in the code. I'm hoping to hook some thermisters up to it to control the valve.

The wide open or completely closed valve sucked. It may be OK in the dead of winter but even with the blower on low it still got too hot in the car when I wanted just a little heat...

__________________
My occupational hazard bein'
my occupation's just not around...
1980 300SD
1980 300SD

Woo Hoo. I figured out how to use the arduino deal to run the blower at different speeds.

Now I can control the water valve and the blower speeds via an IC. That's 2/3 servo function. I guess since I have the basics worked out I need some kind of temp input and some code... Thermister, thermocouple?

WTF. It's like some sort of mild insanity...

__________________
My occupational hazard bein'
my occupation's just not around...
1980 300SD
1980 300SD

And some are curious how the space age system worked, and how it works for the cooling season.

The Arduino is showing a lot of promise

Hammerwerfer

__________________
1985 300DT 241,000 miles
1979 300SD 202,000 miles

Wow,

That's clever.

I changed my center vent pot through the center vent hole and glovebox opening with the instrument cluster in place.

__________________
Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership