As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PERFORMED AN AIR TURN BACK TO MSP. ON TAKE-OFF THROUGH 4000FT FROM MSP OBSERVED FLOW LIGHT ON PRESS PANEL. NO FLOW INDICATION ON BOTH PACKS. OPERATION OF BOTH PACKS WITH NORMAL FLOW. PERFORMED BOTH SINGLE PACK CONFIDENCE CHECKS. OPERATIONS NORMAL. REPLACED SECOND SEGMENT CLIMB SWITCHES S1 -296 / S1-297 AND S1-486. PRESSURIZED A/C TO 7PSI WITH LT PACK AND RT PACK.