LOSS OF CABIN PRESSURE REQUIRES AN EMER DSCNT PROC AND RETURN LAND AT DEP ARPT.

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ON THE LEG FROM PVR TO GDL OUR R AIR CONDITIONING PACK QUIT WORKING. WHEN WE WERE IN RANGE OF GDL I CALLED OPS AND EXPLAINED THAT WE HAD LOST OUR R PACK AND THAT WE WOULD NEED A MECH. THE FLT WAS MET BY A MECH SENT BY GDL OPS AND I EXPLAINED TO HIM THE PROB; AND HE LEFT THE COCKPIT TO TAKE A LOOK AT THE PACK. WHEN HE RETURNED; HE TOLD ME THAT THE R PACK VALVE WAS STUCK CLOSED BUT HE WOULD BE UNABLE TO REPAIR IT. HE SIGNED OFF THE LOGBOOK WITH AN MEL NUMBER AND SAID HE WOULD TELL OPS. A FEW MINS LATER WE WERE GIVEN A NEW RELEASE THAT ALLOWED US TO BE DISPATCHED WITH 1 PACK INOP. SHORTLY AFTER DEP; THE CABIN BEGAN TO CLB UNCTLABLY. WE ASKED FOR AND RECEIVED CLRNC TO DSND BUT THE CABIN REACHED 13500 FT AND THE OXYGEN MASKS IN THE CABIN WERE DEPLOYED. WE RETURNED TO GDL. ONCE ON THE GND; THE CAPT CALLED HOUSTON CTL AND DISCOVERED THAT THEY HAD NOT BEEN NOTIFIED OF ANY PROB WITH THE PLANE. WE WERE TOLD THAT DISPATCH SHOULD NOT HAVE RELEASED US. THE MECH THAT GDL OPS HAD SENT US HAD NOT TALKED TO HOUSTON MAINT AND HAD NO PWR OR AUTHORITY TO SIGN OFF THE PLANE.