What was found
AIRCRAFT WAS NOT GROUNDED: AIR CYCLE MACHINE - PACK R INOP STATUS MESSAGE PACK ACM R CABIN AIR CPRSR R1. ROUGHLY 100 MILES NORTH OF DEN WE HAD A R ACM FAIL, R PACK FAIL, AND R CABIN AIR COMPRESSOR FAIL. WE WERE AT 34,000 FEET AND ATTEMPTED A RESET OF THE R PACK. THE R PACK ESTABLISHED ITSELF AND AFTER 30 SECONDS, FAILED AGAIN. NON-NORMAL CHECKLIST ALLOWS ONE RESET OF PACK. CALLED DISPATCH AND MOC FOR FURTHER INFORMATION REGARDING CONTINUING FLIGHT OVER THE PACIFIC FOR 13 HOURS WITH ONE PACK DECESION MADE TO RETURN TO DFW. EMERGENCY WAS DECLARED AND AIRCRAFT LANDED OVERWEIGHT WITHOUT INCIDENT ARFF WAS ROLLED TO CHECK BRAKES. MAINTENANCE REPLACED RIGHT ACM IAW AMM DMC-B787-A-21-52-02-02A-720A-A.