If you are new to AC repair, then ask a local garage to confirm for you.
If you hit the AC button in the dash, the clutch must engage, spinning the main shaft of the AC compressor.
If AC is On (Clutch engaged) but no cold air and pressure is the same on LO and HI sides, the reed valves are gone.
Early model (2001-2003: check to be sure): Denso
Later model (2004-2006: check to be sure): Calsonic-Kansei
I replaced the AC Compressor on my
1998 528i and posted a DIY below.
Similar procedure for X5:
DIY: 1998 BMW 528i 160K Replacing AC Compressor - Bimmerfest - BMW Forums