As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE, CABIN PRESSURE WOULD NOT HOLD STEADY. SELECTED MANUAL AND STARTED CABIN DOWN MOMENTARILY THEN REVERTED BACK TO AUTO. RETURNED TO MEM AND LANDED WITHOUT INCIDENT. REPLACED SPLIT DUCT AFT OF ACM ON LEFT SIDE. SYSTEM WAS PLACED ON MEL.