got my a/c fixed, I think it still leaks.

sss

That hissing sound is there at all times the compressor is running- it is from the flow of liquid refrigerant through your expansion device. You just are able to hear it better when engine is off. It is completely normal in that the pressures are equalizing through the expansion device- thats why it quits so soon. If it was a true leak- you would not have cool air due to the loss of your refrigerant.