1984 300SD....

So I switched out the CCU (the big electronic controller that has the temp wheel, climate control push buttons and the fan speed) and the problem came back. I say “came back” because for about 25 minutes it seemed to be working perfect. I believe I could hear the system opening and closing vents and redirecting airflow as I was driving. Then about 5 minutes from home the system cut out completely like before - dead air - no response from the fan control. Just like before, I could cycle the system “off” and then back to norm A/C, but with no response from the CCU until the cabin warmed back up above the dialed in temp which would trigger the system back to life with a "click," and it starts cooling / blowing again.

I took the kick panel off below the glove box and wiggled wires like crazy to see if there were any loose connections down there - nothing. I uninstalled / installed the CCU again to see if I could see and broken solders (sp?) on the multi pin connectors that flank the CCU – they looked good.

I did discover that the temp wheel if wiggled would send the CCU into a clicking frenzy. Even with everything mounted up tight - if you give it a little grab and jiggled it during cool down you can make it click like a machine gun. Weird huh.

So - here is my latest theory. When it did work when I first swapped the CCU (hopefully I was not imagining anything), does the system in fact vary airflow through different parts of the dash automatically when cooling? Does the system direct airflow one way for max cooling then switchover to another path for maintaining the temp? If so, I don’t think my system gets that far in the process. In my situation the fan speed does decrease to a lower setting as it cools down, then “click” it shuts down, but the airflow is never changed to other vents.

I'm wondering if it is at that point (when it should change airflow from rapid cool to maintain) perhaps there is resistance when it tries switching the vents, which is shutting the CCU down? If that is probable, what part of the system controls the opening and closing of vents when the A/C is running? Is it a relay?

I'm frustrated as can be - when it was working (though briefly) it was awesome.

For more history – here is the original thread:

'84 300SD W126 - A/C Question - the saga continues

__________________
~shell
As of 2/2010:
2001 CLK55 0o\=*=/o0
13.6 @ 106mph
10K mi
1984 300SD
260K mi and going and going...
97 S600
46K miles
1991 Sentra SE-R (extremely dorked with)
www.se-r.net