A B737-800 WAS DISPATCHED AND OPERATED 8 DAYS WITH A PAX SVC UNIT REPLACEMENT MISSING THE REQUIRED OXYGEN CANISTER.

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RECOVERING FROM A SEVERE COLD WITH LITTLE BIT OF SLEEP WITH ONLY 2 MECHS ON DUTY THAT DAY (ME AND 1 MECH) WITH AN ABNORMAL WORKLOAD THAT DAY DUE TO GNDED ACFT AND MOVING ACFT AND WORKING THROUGH FLTS WITH MULTIPLE ISSUES; ALSO RESEARCHING FOR PARTS AND TOOLING NEEDED FOR THE GNDED ACFT. BTWN ALL THIS; WE HAD AN ACFT COME IN THE MORNING RUSH WITH AN INOP (PAX SVC UNIT). THE PAX SVC UNIT OXYGEN MASK WON'T STAY STOWED DUE TO 1 CLIP BROKE OFF; SO WE HAD TO SECURE THE OXYGEN MASK DOOR WITH TAPE AND DEFERRED AND BLOCKED ALL 3 SEATS AT THAT ROW. AFTER THAT; I ORDERED NEW PAX SVC UNIT. LATER THAT DAY; 45 MINS BEFORE OUR SHIFT IS OVER; THE SAME ACFT ARRIVED BACK; AND THE NEW PAX SVC UNIT BECAME AVAILABLE WITH A SVCABLE TAG SHOWING THAT PAX SVC UNIT HAS BEEN BENCH CHKED AND SIGN OFF BY QUALITY CTL; WITHOUT ANY SPECIAL NOTES IN THE COMMENTS SECTION ON THE TAG. AFTER VERIFIED IT HAS THE CORRECT PART NUMBER AND ALL OTHER INFO ON THE TAG; THEN DUE TO CHANGE OF ACFT ROUTING I FELT WE NEED TO CHANGE THE PAX SVC UNIT TO CLR THE DEFERRAL AND GAIN BACK THE 3 SEATS THAT CAN BE USED FOR PAX; WITH ONLY 25 MINS FOR DEP. I RUSHED TO PULL UP AND PRINT OUT THE MAINT MANUAL REF FOR THE REMOVAL AND INSTALLATION. MEANWHILE; THE PRINTER WAS JAMMED; SO I SKIMMED THROUGH THE MAINT MANUAL ON THE COMPUTER SCREEN AND FOCUSED ON THE OPS CHK AFTER THE INSTALLATION; BTWN TRYING NOT TAKING A DELAY AND NOT DISTURBED THE BOARDING OF THE PAX WE DID NOT NOTICE THAT THE NEW PAX SVC UNIT WE INSTALLED IS MISSING AN OXYGEN GENERATOR CANISTER. AFTER WE CHKED LIGHTS AND GASPER AIR; I SIGN OFF THE ITEM AND CLRED THE DEFERRAL; THEN AFTER 8 DAYS IT WAS DETERMINED THAT THE PAX SVC UNIT WE INSTALLED MISSING THE OXYGEN GENERATOR CANISTER WHILE THE ACFT IN GND WHERE THE OXYGEN CANISTER WAS ULTIMATELY REPLACED AND THE ACFT RETURNED TO SVC.