What was found
THE FLIGHT CREW REPORTED WHILE AT FL360 - FL400 NO CABIN TEMPERATURE CONTROL FROM COCKPIT CONTROLLER IN AUTO OR MAN CABIN TEMP RANGED FROM 20C TO -10C OVER 3.7 HOUR FLIGHT. THE MAINTENANCE TEAM DISCOVERED A LOOSE CONNECTION ON CABIN PROPORTIONING VALVE AND ALSO FOUND CABIN AND COCKPIT TEMP CONTROL VALVE LINES SWAPPED. CORRECTED PNEUMATIC LINE INSTALLATION. OPS CHECKS SATISFACTORY. NOTE: IT WAS DETERMINED THIS AIRCRAFT RECENTLY RETURNED TO SERVICE FROM A LARGE MAINTENANCE EVENT BY A MAJOR MRO SPECIALIZING IN THIS AIRFRAME. A CAR REPORT WAS REQUESTED FROM THIS MRO.