As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
Could not control pressurization after takeoff in all modes. Overweight landing made at 175,000lbs. back at MSP.ACTION TAKEN:R&R'd L/H flow control valve pressurized A/C ops check normal A/C OK for service. Also secured ground wire. Overweight landing inspection accomplished no defects noted.