Chris thank you for your input, very helpful.

From what I know, the AC fan turns on and off on high pressure side, at least that's what the diagram shows and where the wires run from.
The compressor cycles off during acceleration.
The heater valve I may suspect is NOT completely off, i.e. when I switch on the heater fan with the engine having run for some time, I feel a slight portion of warm air leaving the vents, but it dissipates quickly and after that it blows outside air. Need to check it, I understand.
The system doesn't work very well - at least not as cool as before.

NOW I have an idea. I recently replaced a primary engine-driven fan with an electric one off a 960. It only comes on when the coolant temp sensor tells it to, i.e. there is no longer constant air flow through radiators like it was with the mechanical fan.
With the mechanical fan, the AC fan almost NEVER turned on. Now it runs every time I switch on AC (cycles on and off regularly).
Could it be just insufficient AC condenser cooling, what do you think?

I believe I should try switching on the primary fan every time I toggle the AC button and see what happens.

Thank you again for your comments.
Andrew