What was found
HAD ZERO DUCT PRESSURE LEFT SIDE CLIMBING OUT ACARS MSG LEFT PACK OFF WORKS ON APU BLEED AIR. ENG RUNNING NORMAL, LOSS LEFT PACK, AND LEFT PRESSURE WAS AT 0. FLIGHT CREW DEBRIEF. SAME WAS BEFORE. PERFORM HEALTH CHECK PER MM36-11-00-700-801 ON #1 ENGINE. REPLACED HIGH STAGE REGULATOR, BLEED AIR REGULATOR AND PRSOV PER TASK36-11-00-700-801. BLEED SYSTEM OPS CHECKS NORMAL AT IDLE. ROTABLE PARTS CHANGE WAS INDICATED - TT # 1043580 SN OFF 3624 TT # 1185654 SN OFF 3721 TT # 1038853 SN OFF 7379 IPC REFERENCE # 36-11-07-02A VALVE, PRESSURE OFF 29-3612-9-0004 3624 ON 29-3612-9-0004 5395 REGULATOR, HI S OFF 29-3611-9-0006 3721 ON 29-3611-9-0006 7202 UPDT PARTS TRANSACTION. ROTABLE PARTS CHANGE WAS INDICATED - TT # 1038853 SN OFF 0339 REGULATOR, BLEE OFF 29-3611-9-0005 0339 ON 29-3611-9-0005 7379