Thanks for the information M.B. DOC.

Well, I still don't have a clear "fix."

I noticed that when I start the car I can hear the A/C Clutch and cooling fans kick in for about two seconds before dropping out.

I can ground the signal at the pressure switch on the drier and make it engage and the car will cool nicely.

Since the signal to the drier comes from the CCU in the dashboard, the problem would appear to be in the CCU. In examining the readings using the CCU tests supplied by M.B. Doc, there were no unusual readings that I could see.

I went to my shop and shared the symptoms and CCU readings with them.

Upon consulting the wiring diagrams we saw that the MAS controller sends some signals to the CCU that could possibly cause the CCU to de-select the A/C compressor engagement signal sent to the drier switch.

It was recommended that I use my LED reader to pull the codes from the MAS Controller to see if there was anything unusual there.

Upon reading the codes I found the following:

Code 11: A/C compressor engagement signal missing (87Z)
Code 13: Excessive A/C compressor clutch slippage

Once I cleared those codes it started working just fine! It COULD well be a coincidence that it started working after I cleared the last code from the MAS controller because there have previously been times that I could not make it fail while I was troubleshooting the problem...

Presuming the problem will soon return, I will re-read the MAS codes at that time...

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