I have read everyone's posts regarding all of the CCU problems but none of them seem to match waht I have observed. Here is what I have found so far.

The control unit has no functionality whatsoever the buttons do not change moods, the temp wheel does not alter temperature and the fan controls do not change blower speeds.

As for the blower, no blower operation exists. I only have air coming from the defrost vents with no blower function. I have no A/C contol and the A/C unit does not even cycle on/off.

I have replaced the ignition switch feeling that it might have had something to do with it because the system worked fine when I got the car and then one day it just quit. I have replaced the voltage regulator and I have swapped out the CCU, all with no change.

At the fan plug up under the winsheild cover I have found the following:
Black wire to ground,, Red wire constant +12v
Yellow wire with fan on high +2.25v, on low +1.5 v and on AUTO +0.0v
Fuse #5 has +12v, Fuse #12 0.0v and Fuse D +12v
I also pulled the glove box and found good vacuum and have no other issues engine vacuum finne, door lock system fine etc..

DON"T KNOW WHERE TO LOOK NEXT
1988 260E if it matters

Your post confuses me a little bit but I'll try to help:

So your blower motor does not come on at all?
Or it does come on sometimes or blow out certain vents only?
This leads me to believe that it is a fuse or something simple like that. Have you inspected the fuses? Also why did you replace the ignition switch?
How did you measure the voltages at the fuses? The information I have suggests that fuse 7 is the fuse for the climate control system. I would look at this fuse, take it out and verify that it is not broken/cracked.

Good luck!

__________________
Daily Driver: 02 E430 4MATIC
In the family: '03 E500 // '04 ML500 // 64 220SE

The blower does not work, it will spin if direct current is applied.


All I get is hot air coming out of the defrost windsheild vents.
I used a digital volt meter to check voltages as well as the fuses.
I replaced the ignition switch because I had read that over time they can go bad causing an on again off again functionality and I wanted to eliminate as many possible problems as I could.

OK.... I have just walked back inside from changing out Fuse #7 and as I am sure you knew it would EVERYTHING is working. OH MY GOD!!! do I feel stupid. Thank you very much for pointing out what was right in front of me. On a somewhat related note , which button selection puts air down at my feet?? I tried them all but could not feel anything.

Again thank you responding.