As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
UNABLE TO PRESSURIZE AIRCRAFT AFTER TAKEOFF. AIRCRAFT RETURNED TO FIELD. *S/D* ACCOMPLISHED CHECK OF BOTH PACKS AND ENGINE PRESSURE BLEEDS. PRESSURIZED ACFT TO 6 PSID OFF ONE PACK. CHECKED OUTFLOW VALVE HEATER GASKET RESISTANCE. ALL SYSTEMS PERFORMED NORMAL.