What was found
(B-18706) AFTER TAKE OFF, FLIGHT CREW REPORTED THAT IT WAS UNABLE TO CONTROL F/D TEMPERATURE, RESULTING IN HIGH F/D TEMPERATURE.(43 CENTIGRADE) EICAS ECS-REAL PAGE SHOWED THAT PTC-A IN CONTROL & ALL 3 PACKS OUTLET TEMPERATURE ABOUT 57 CENTIGRADE. THERE WAS NOT ANY RELATED FLIGHT DECK EFFECT AND EICAS MESSAGE. PERFORMED PACK RESET & SELECTED PTC-B FOR PRIMARY CONTROLLER BUT STILL IN VAIN. FLIGHT CREW CONSULTED WITH CHIEF PILOT, JC & MOC THEN DECIDED TO DIVERT. AFTER ACFT ARRIVED, PTC-A C/B PULLED & TRANSFERRED TO PTC-B. ALL PACKS OUTLET TEMP BACK TO 3 CENTIGRADE. CONFIRMED PTC-A & PTC-B CANNOT SWITCH AFTER PTC-A C/B PUSHED IN. REPLACED PTC-A & ALL 3 PACKS OPERATION NORMAL. PTC-A HAS BEEN SENT TO MANUFACTURER HAMILTON SUNDSTRAND FOR SHOP REPORT.