A B737-300 WITH 'A' AND 'B' AUTOPLTS INOP WAS REPAIRED WITH AN ACCESSORY UNIT REPLACEMENT. TECHNICIAN FAILED TO ADVISE MAINT CTL OF THE REPAIR AND THE NECESSITY TO RECERTIFY CAT III STATUS OF ACFT.

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ACFT WAS COMING IN WITH BOTH AUTOPLT CHANNELS ON MEL. MAINT CTL HAD REQUESTED THAT WE TRY TO GET ONE SIDE WORKING. I MET THE ACFT WHEN IT ARRIVED. I HAD REVIEWED THE HISTORY OF THE AUTOPLT SYS BEFORE MEETING THE ACFT AND HAD DETERMINED TO CONCENTRATE ON THE 'B' SYS. I WENT INTO THE FLT DECK AND NEITHER WOULD ENGAGE. DFCS BITE DID NOT HELP. I DECIDED TO TRY CHANGING AN INTEGRATED FLT ASSEMBLY UNIT SINCE IT IS USED BY BOTH SYS. AFTER FINDING OUT BITE DOESN'T TEST THE UNIT; I REMOVED THE BOX AND SPRAYED THE PINS ON THE RACK AND BOX ITSELF. I REINSTALLED THE BOX AND WENT BACK INTO THE FLT DECK. BOTH CHANNELS OF THE AUTOPLT NOW WORKED NORMALLY. DUE TO THE HISTORY OF THE 'A' SYS; I THOUGHT IT BEST TO LEAVE 'A' SYS AS AN MEL ITEM AND CLR THE MEL ON THE 'B' SYS. I DID THE NECESSARY PAPERWORK AND RELEASED THE ACFT TO THE CAPT. ABOUT 2 HRS LATER; I REALIZED THE INTEGRATED FLT ACCESSORY UNIT WAS A HYD COMPONENT. I IMMEDIATELY NOTIFIED MAINT CTL SO THEY COULD HAVE THE ACFT RECERTIFIED TO CAT III STATUS.