As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FLIGHT, THE CREW REPORTED RT ENVIRO FAIL AND CABIN ALT HIGH. SINCE THE FLIGHT LEVEL WAS RESTRICTED TO 9500 FT THE CREW PERFORMED AN AIR-TURN-BACK. MX REPLACED THE LT PRSOV BUT THAT DID NOT FIX THE PROBLEM. MX INSPECTED THE SYSTEM AND FOUND A LOOSE TEST LINE AFTER TIGHTENING THE LINE THE SYSTEM OPS CHECKED GOOD AND THE AC WAS RETURNED TO SERVICE. (K)