Would you be able to help me with this?
I'm having the same problem with an Astra (2000/2001) I got from ze dad.
Just google Astra AC pressure switch. You can do a diy fix/bypass or replace the switch without losing gas.
http://www.astraownersnetwork.co.uk/showthread.php?t=92233
http://www.jeepforum.com/forum/f11/c-pressure-switch-bypassed-car-now-like-fridge-p-549324/
http://wiki.answers.com/Q/The_air_c..._full_of_refrigerant_what_else_could_be_wrong