AIR CONDITION STARTS ON RANDOMLY AFTER SWITCH ON IN PASSAT 1998

first, of course, make sure the system is not low on refrigerant (r134a) (check low side pressure) ...if thats ok then there is a relay (electronic module) that fails frequently .. the nature of this failure is that at times the air conditioner wont work at all .. then other times it works fine .. eventually it will faill completely ..if that sounds like your trouble then you can get at the relay by removing the panel at the left side of the dash (normally hidden by the door) (snaps off) ..you will see the fuse panel and behind that the relays .. the relay is marked "384" .. it costs about $50 .. i have been able to repair them and have taken photos to help in that repair if you are electronically handy ..make sure you observe how it comes out .. its difficult to figure out which way it plugs in unless you mark which way is up .. ..