I dont belive the pressure switch is at fault,
If running the compressor for 1 min cause over pressure and vented then this tells me there is definatly a blockage in the system,

You can bridge the pressure switch to see if it cuts in, this will at least tell you if it is the switch tripping it out but it 100% has a blockage that needs to be sorted,

Vaccum it down for around 2 hours "should" remove any sludging,

I work on hgv's mainly so cant coment regarding hardware fitted to this particular car but ac is ac,

And as said above... Watch what your doing with this stuff, its not nice stuff,
Ive had a pipe on a eurorider coach blow before... 11000 kg's of gas exploding out the back of the coach as i was stood there!!!!!! Scary stuff!! Could of quite easily ended in disaster!