Well…
I must start by saying that it has been "Hotter than Hades"
around here !
I just got my 1983 SD this week, and I am overall pleased.
However I am trying to wrestle with some climate control problems (who would have guessed! ) (lol) The car is cooling real good, but with the air only blowing from the side vents and the defrost vents. Also sometimes the fan will just turn off, and I have to press the climate control buttons in random order to get it back blowing. I did some searching this week, and this morning this is what I found. The diaphragm that controls the major flow of the center vent will hold a vacuum. It has a green tube from the diaphragm to a switch labeled #4. If I by-pass the vacuum manifold at these switches the damper holds, if I try to just by-pass the #4 switch, it will not. Interestingly though, when by-passed, and the center vents working, the air seems to not be as cold. It feels colder though once the fan stops and I get it running again. I know that I probably have a nasty little German gremlin in the system, but if anyone else has any thoughts on this, I will try it.
One other interesting thing, when the button for the upper vents is pressed, I do not get any voltage at the #4 switch.

Hope to hear some feedback,
Thanks!
Robert

Step one: Check for good vacuum supply to the system from the vacuum pump on the engine -- no air from the center vents is the default setting for the climate control.

Also, check the fuse for the climate control, although if you have AC I suspect that isn't the problem, you usually get only full heat with the fuse bad.

If you have good vacuum, or if you can supply good vaccuum with a MitiVac or similar pump, then the pushbutton control unit is toast.

My guess would be a vacuum supply problem, either broken, plugged, or leaking lines, or a dead vacuum pump.

The supply for the sustem is the green plastic line in the engine compartment, next to the brake booster.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

It's fixed !
I went on a junk yard sabbatical this morning, not even looking for a climate control unit, but when I stumbled across one that was like brand new, I had to get it.
Came home, and switched the units, and voila! Everything work great.
The thing that was making me suspect the control unit was the non-switching of the #4 valve. Once I changed the units out, with the side console panel removed I could hear all of the valves working in each of the different modes.
I get a big pat on the back today!
Robert