Suddenly no ground to AC

[filp]

Hi,

1992 300D.
Out of the blue my AC turned off at a stop light, then came on a minute later.
The next day it worked, but cut off after a few minutes of driving. Now it works for a minute then dies. Comes on for a few seconds while driving.
I performed the diagnostic from FSM.
There is no ground from the CCU (pushbutton unit) to pigtail on high pressure switch. I tested that with 3 different CCUs.
I replaced the evaporator sensor, no change.
What should I do next?
AC charge is good, checked. If I provide ground to high pressure switch, everything is cold.
Aux fans are operating good. Belt is not slipping.
Thanks