As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD - FLT 1214 - EN ROUTE ORD-YYZ, CABIN PRESSURE CONTROL MESSAGE ILLUMINATED IN CABIN. UNABLE TO CONTROL CABIN PRESSURE IN THE MANUAL MODE. RETURNED DFW AND LANDED WITHOUT FURTHER INCIDENT. REPLACED LEFT SIDE PACK. REPLACED PRIMARY AND SECONDARY HEAT EXCHANGERS AND LEFT SIDE CYCLE MACHINE. ACCOMPLISHED LEFT AND RIGHT SIDE ENVIROMENTAL CONTROL CHECKS. SYSTEM GROUND CHECKED NORMAL OPERATION. (M)