What was found
AIRCRAFT WAS GROUNDED: PILOT REPORTS PRESSURIZATION FLOW LIGHT ILLUMINATED AT 26,000 FEET, HAD EXITED ICING 5 MINUTES PREVIOUS, BOOTED THE TAIL AND WHEN THE TAIL FINISHED, THATS WHEN THE PRESSURIZATION ISSUE BEGAN. MAINTENANCE FOUND LH PACK PRESSURE NOT REGULATING. REMOVED AND REPLACED AC PILOT PRESS REG IAW AMM 21-31-11 AC AND PRESS REG VALVE IAW AMM 21-31-01. OPS AND LEAK CHECK GOOD. SEE SDR AALA201905139032.