Before you change anything, try diagnosing the pressure switch (aka triple switch) by bridging the contacts.
From memory, the aircon triple switch is fed a signal from the climate panel which enables air con if the climate panel is calling for cold air. It will break this circuit if the system pressure is below the minimum pressure or above maximum pressure. This wire is colour coded black with a white tracer at the triple switch.
This signal then feeds an input to the engine ECU. If you've got a code reader that shows live data I believe you can read the level of this input from the ECU. Output from the engine ECU feeds the air conditioning relay K60 so the engine ECU can veto the use of air con in certain cnditions.
There is also a coolant temperature switch that breaks the ground connection to the air con compressor if the coolant gets too hot. This would leave the fans operating as normal, so guessing this isn't the problem.
The triple switch also has another contact (Brown / Brown with white tracer) which brings the fans up to full speed at a certain pressure.
I would try bridging the black / white wires into and out of the triple switch next.