As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMBOUT, LOST AIRFLOW FROM LEFT PACK. RIGHT PACK ON MEL. UNABLE TO MAINTAIN CABIN PRESSURE. FLIGHT RETURNED TO ATL AND LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED RIGHT FLOW CONTROL VALVE AND RIGHT PRESSURE REGULATOR VALVE. CLEARED MEL. PROBLEM WITH LEFT PACK COULD NOT BE DUPLICATED. SYSTEM OPERATIONAL CHECK OK.