What was found
FLT#977, BOS-LAS. (AIRCRAFT DIVERTED TO ORD) 'AFT CABIN INDICATED 54* IN FLIGHT; PERFORMED OPERATIONAL TEST OF THE PACK TEMP CONTROL SYSTEM IAW AMM 21-61-00-710-001. TEST REVEALED TRIM AIR VALVE 12HK AND 13HK FAILED. WHEN TWO TRIM AIR VALVES FAIL THE HOT AIR VALVE WILL AUTOMATICALLY CLOSE. RESET ACSC 2 (57HH) AND RAN PACK TEMP CONTROL SYSTEM TEST AGAIN. ALL FAULTS CLEARED. OPERATED BH PACKS IN ALL RANGES COLD TO HOT AND AFT CABIN.