I had my a/c serviced now the rear unit hissing. on 2000 Ford Expedition

I turned a/c unit on to defrost and a fine mist of freon came out of the air vents in the front.Within seconds i heard a hissing noise from the rear unit. Do I need to replacing everything in the rear of the truck? The system is blowing totally warm now.

Asked by for the 2000 Ford Expedition
possible leak