i was quoted 800 quid to get mine fixed,and that was just having the compressor changed and then a regas,obviously the price wouldve gone up if they found anything else wrong,in the end i got hold of a 2nd hand compressor,then my mechanic found the clutch wheel of the compressor sitting happily in the engine tray,robbed the clutch wheel from the new one and got it working for the princely sum of 30 quid and no need for a regas,it might be something as simple as this or it might not,hopefully it wont cost you both arms and a leg.