AFTER REPLACING THE LEFT FMC DUE TO LOW AIR FLOW ON A B767-300; MECHANIC IS INFORMED BY MAINT CONTROL THE ROBBED CDU HE INSTALLED DID NOT MEET EFFECTIVITY FOR THAT ACFT. PLANE HAD ALREADY DEPARTED.

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ACFT WAS A CREW REFUSAL FOR L FMC CDU FAIL; DUE TO LOW AIR FLOW TO FMC CDU. REPLACED CDU IN ACCORDANCE WITH AMM 34-61-02 WITH MR ROBBED PART FROM ACFT X. CHKED EFFECTIVITY VIA COSMO/SCDREC DISPLAY AND UIPC REF 34-61-02-001. ENRTE LINE MAINT NOTIFIED SUPVR THAT MULTIPURPOSE HYBRID FMC/CDU IS TO BE INSTALLED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THE LOW AIR FLOW WAS CAUSED BY EXCESSIVE DUST BUILD-UP ON THE LOWER SIDE OF THE B767-300 FMC-CDU; WHERE THE UNIT MATES WITH THE COOLING AIR HOSE AND A PLIABLE O-RING GASKET SEAL; ABOUT THE SIZE OF A SILVER DOLLAR. REPORTER STATED THE FAILED CDU WAS BLANKING OUT FROM OVERHEATING AND WAS SO HOT THEY COULD NOT HOLD THE CDU IN THEIR HANDS. HE DID NOT WANT TO REINSTALL THE SAME UNIT; EVEN THOUGH THEY HAD REMOVED THE DUST THAT WAS CAUSING THE COOLING BLOCKAGE; AND DECIDED TO REPLACE THE FMC-CDU. REPORTER STATED HE HAD CROSSED REFERENCED THE MAINT MANUAL; THEIR FLEET EQUIPMENT LISTING AND VERIFIED THE PART NUMBER EFFECTIVITY FROM THEIR STORES IPC; THAT STATED THE CDU WAS ACCEPTABLE FOR USE ON 'ALL' THEIR B767-300 ACFT. HE LATER FOUND OUT AFTER BEING INFORMED THE INCORRECT CDU HAD BEEN INSTALLED; THAT FURTHER DOWN THE IPC LISTING AND AFTER SHOWING EFFECTIVE FOR 'ALL' B767-300'S; WAS ANOTHER LISTING FOR CDU MOD CHANGES THAT HE HADN'T NOTICED. ONLY PROBLEM WAS; THERE WASN'T ANYTHING ASSOCIATED WITH THE 'ALL' LISTING; NO ASTERISK OR OTHER IDENTIFIERS TO INDICATE HE SHOULD LOOK ELSEWHERE FOR POSSIBLE EXCEPTIONS TO 'ALL'. REPORTER STATED THE CARRIER'S CHIEF INSPECTOR TOLD HIM IN A MEETING; THAT HE HAS TRIED TO GET THE ENGINEERING GROUP TO 'FLAG' THE 'ALL' CATEGORY; BUT ENGINEERING HAS REFUSED TO CHANGE ANYTHING IN THEIR CURRENT PRACTICE TO HELP MAINT TO INSTALL THE CORRECT PART. REPORTER ALSO STATED THE TERM 'HYBRID' WAS A MISNOMER WHEN REFERRING TO THE DIFFERENT FMC-CDU'S; BECAUSE THESE ARE ACTUALLY MODIFIED (UPGRADED) UNITS; THAT HAVE IMPROVED SOFTWARE ALERT AIDS FOR FLIGHT CREWS. THE MODIFIED AND UNMODIFIED UNITS ARE NOT INTERCHANGEABLE.