As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER T/O WITH PACKS ON, THE FLOW LIGHT WAS PRESENTED,THE LEFT PACK DROPPED TO ZERO AND THE RIGH PACK WAS SHOWING 20 PSI. THE LEFT PACK WAS NOT POSSIBLE TO RESTORE SO WE PROCEED TO PRESSURIZE MANUALLY,WHICH WAS ALSO IMPOSSIBLE.ON FINAL THE LT PACK WAS RESTORED. RT PACK FLOW CONTROL VALVE WAS REPLACED IAW AMM 21-31-02 IN LT PACK WAS REPLACED NEUMATIC PRESSURE REGULATING VALVE. PRESSURIZATION CHECK WAS ACCOMPLISHED IAW AMM 21-00-00 PAG 504. SATISFACTORY RESULTS.