As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU DUCT PRESSURE SURGING 5 -15 PSI WITH PACKS RUNNING. AFTER TROUBLESHOOT AND RESET APU BLEED AIR AND CONTROL CB. DUCT PRESSURE NORMAL, PER MCC REQUEST APU PNEUMATICS DEFERRED TO MDDR 139986, CAT C, MCC TODD C LC 12:12Z, DDG 49-11-01-01. REPLACED APU SURGE CONTROL VALVE AND RUBBER DUCT, IAW AMM 49-53-01. OPERATIONS CHECK AND LEAK CHECK GOOD.