I missed the question about the auxiliary fan activation through the pushbutton control unit N22.

The diagnostic manual says to hold both buttons for >10 seconds. It takes at least 12 seconds for my N22 to activate the fans.

I don't know the failure mode of the fan in your car, as the controller is different than mine, but on mine, if the current draw is not correct (too high or too low), the fans will "kick" about once every six or eight seconds but not quite start. I would not be surprised if the failure mode in yours is either exactly the same or completely different, but it doesn't hurt to go watch them. If the fans don't run when they are needed, the high side pressure and temperature will skyrocket.