What was found
APPROXIMATELY 4 HOURS INTO FLIGHT, RT PACK TRIPPED & UNABLE TO RESET. ACFT WAS DISPATCHED WITH LT PACK INOPERATIVE. RT PACK HAD A HARD TIME MAINTAINING DESIRED TEMP, KEPT GOING FROM VERY HOT TO VERY COLD WHILE AIRBORNE. NO RAPID DECOMPRESSION EXPERIENCED. PERFORMED AMM TASK 21-51-00-705-184 OF THE PACK ZONE SYS HEALTH CHECK. WHILE TROUBLESHOOTING THE SYS, FOUND THE PACK STBY CONTROLLER FAULTING IN POSITION 1 & 2. R & R PACK STBY CONTROLLER IAW AMM 21-51-14-004-001. PERFORMED BITE TEST. OPERATIONS CHECKED GOOD. NO FURTHER DEFECT NOTED.