What was found
AT CRUISE, FA REPORTED THAT AFT CABIN WAS TOO HOT. WE TURNED DOWN THE AFT CAB TEMP, BUT THE AFT SUPPLY DUCT TEMP STAYED HIGH-AROUND 32 DEGREES. AFTER SOME TIME, IT DECREASED TO AROUND 28 DEGREES, BUT FA REPORTED AFT CABIN STILL HOT, WE TURNED OFF TRIM AIR PER CHECKLIST, AND AFT SUPPLY DUCT & AFT CABIN COOLED. GROUNDED - YES. FOUND AFT CABIN TEMP SENSOR FILTER CLOGGED WITH OMF MAINTENANCE MESSAGE 21-55341. CLEANED FILTER AND ACCOMPLISHED IFIM 21-51-00-810. OPS TEST NORMAL.