As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF SWITCHED BLEEDS TO ENGINES AND GOT RT PACK HI PRESS WITH BURNT SMELL IN A/C. FOLLOWED QRH TO RESET BUT DID NOT, ALREADY SINGLE PACK. FINALLY GOT TO RESET AFTER STARTING APU AND SWITCHING BLEEDS. AIRCRAFT RETURNED TO ATL AFTER T/O. FLTS 4856, 4866 CX.