UPDATE:

Well, the problem is still unresolved and my level of frustration is rising...

Being confident that the CCU was the culprit, I sent it to ProgRama to be repaired. They returned it with "No problem found."

When I first start the car, the A/C will engage for 2 or 3 seconds and then it is over... Turning the A/C off and on at the CCU does not generate another 2 seconds if operations. Restarting the car will cause the compressor to work each time for 2 or 3 seconds...

The codes 11 & 13 (mentioned above) were successfully cleared from the MAS controller several days ago. Today I checked the MAS codes and the 11 code (A/C Compressor engagement signal missing (87Z)) has returned. I cleared it and it did not immediately return.

Occasionally, while driving, the A/C will engage and start cooling. When this happens, it usually continues to function for the remainder of the trip.

So, what do I do now? Replace the MAS Controller?
Where is the thing? Perhaps I will inspect it for cold solder joints.

__________________
02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)