Why is the Air conditioning pump not working on Vauxhall Astra?

Possible causes could include:

Failed air-con on/off switch.

Wiring fault.

Compressor clutch fault.

Blown fuse.

No gas in system.

the clutch on the compressor has a fuse and it was blown.

i soldered across the fuse and the clutch is now working.

also if there is not enough gas the clutch will not engage as well.