I have a 1996 Ford Galaxy. Last year it had a new compressor and heat exchanger, yera before new a/c pipework. It has been regassed 3 times and just keeps loosing the charge, there are no obvious signs of any leaks. There is (occasionaly) a hissing sound which sounds like it is coming from behind the passenger side dash. Anyone know if this could indicate a problem with the evaporator. If it is the evaporator does anyone know if this requires any specialist knowledge/equipment to replace? Also, the a/c display flashes to indicate a fault. Would the problem above cause the display to flash or is there likely to be another problem?