The air conditioning in vauxhall astra is not working it is full of refrigerant what else could be wrong?

Unplug the low pressure cutoff switch and short the harness with a jumper wire. If the AC compressor cuts on and works, then the electrical portion is good and the low pressure switch is the fault. If not, check the fuse(s) and the relay. Also, you say it's full of refrigerant gas: make sure it's not over-full. That would prevent proper operation as well.