Starting last summer, my car started making a strange hissing noise when the a/c was on. It started out as an intermittent thing; sounding something like a a turbo spooling up and ending with a sound like the valve on an airhose being slowly closed. It didn't seem to effect the temperature of the a/c. Soon, however, it became a continuous hiss; vaguely metallic but largely like an airflow type sound. It only occurs when the a/c compressor is on. The strange thing is that the compressor seems to run year-round; even when it was far below zero last winter I would hear the clutch engage and the hiss would start. The book symbol has been going on and off intermittently; and now the a/c doesn't blow cold at all anymore. The RAVE cd said that a low charge in the system could cause a hiss; so today I had the a/c recharged. I just drove the car back from the mechanic and its still not blowing cold at all and the hiss is still there. Thoughts? Its starting to get hot and I can't drive around in an a/c-less car all summer! I hope its not the compressor or some kind of a leak somewhere.