As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING THE CLIMB CHECKLIST, THE CREW NOTICED THAT THE CABIN PRESSURE HAD NOT STARTED TO CLIMB. IT CONTINUED TO READ 0 FPM ON CLIMB RATE. AFTER REACHING 20,000FT THE INDICATION WAS STILL ZERO AND THE CREW ELECTED TO RETURN TO FIELD. THE AIRCRAFT LANDED BACK AT MKE WITHOUT INCIDENT. MAINTENANCE PERFORMED THE ADJUSTMENT/TEST OF THE PRESSURIZATION CONTROL SYSTEM IN AUTO AND MANUAL MODES IAW AMM 21-31-00. OPS CHECK GOOD.