As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT N2726, THE CREW REPORTED THAT ON TAKEOFF THEY LOST PACK 2 (PACK VALVE CLOSED) WOULD NOT RESET. DECLARED AN EMERGENCY & RETURNED TO DEPARTURE. LANDED WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. INSTALLED DUCT ON NR 2 HEAT EXCHANGER. NR 2 PACK OPS CHECKED GOOD AMM 21-51-00. AIRCRAFT RETURNED TO SERVICE.