A B757-200 MECHANIC REPORTS ON REALIZING HE HAD INSTALLED THE RIGHT RECIRC FAN WITHOUT THE REQUIRED ORIFICE PLATE. CARRIER ENGINEERING HAD NOT CHANGED THE PART NUMBER OF THE MODIFIED FAN.

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WHILE RESEARCHING A PROB ON ACFT X; ITEM 1; I REALIZED THAT WHILE I WAS REPLACING THE R-HAND RECIRCULATION FAN ON ACFT X; I MISTAKENLY INSTALLED THE NEW FAN PART NUMBER X; WITHOUT INSTALLING THE ORIFICE PLATE ITEM #3 PART #Y; I MISTAKENLY THOUGHT THAT THE NEW TYPE FAN HAD ENGINEERING ORDER ACCOMPLISHED AND THE ORIFICE PLATE WAS PART OF NEW FAN ASSEMBLY. READ MAINT PROGRAM CONTROL INFO MORE CAREFULLY; AND WORK WITH ENGINEERING DEPT TO CLARIFY ENGINEERING ORDER ACCOMPLISHMENT ON COMPONENT VERSUS ACFT FOR FUTURE INSTALLATIONS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED ENGINEERING HAD NOT DIFFERENTIATED THE MODIFIED RECIRC FANS FROM THE UNMODIFIED (OLDER) TYPE BY USING A DIFFERENT PART NUMBER; DASH NUMBER OR EVEN SERIAL NUMBER ON THE FAN UNIT; OR IN THEIR ILLUSTRATED PARTS CATALOG (IPC). HIS COMPANY WANTED TO MAINTAIN INTERCHANGEABILITY OF THE RECIRC FANS ON THE B757'S. HOWEVER; THE HIGHER VOLUME OF AIR FLOW THE MODIFIED RECIRC FANS PRODUCED WERE FOUND TO ALSO INCREASE THE NOISE IN THE ACFT. SO; AN ORIFICE PLATE; OR FLOW RESTRICTOR; WAS INSTALLED IN THE HOUSING OF THE FAN UNIT UNDER AN ENGINEERING ORDER ACCOMPLISHED IN THE SHOPS. THIS ORIFICE (RESTRICTOR) PLATE MAY NOT BE NOTICED BY MAINT PERSONNEL INSTALLING THE RECIRC FAN. BUT; MANY OF THE NEWER FAN UNITS STILL HAD NOT GONE THROUGH THE SHOPS FOR THE ORIFICE PLATE INSTALLATION. WITHOUT ANY DIFFERENT NUMBERS TO DISTINGUISH BETWEEN THOSE WITH OR WITHOUT THE PLATE; REPORTER INSTALLED THE FAN. HE LATER REALIZED THE FAN HE INSTALLED STILL REQUIRED AN ORIFICE PLATE BE INSTALLED IN THE DUCTING TO COMPENSATE FOR THE INCREASED AIR FLOW. REPORTER ALSO STATED THAT PART OF THE PROBLEM WITH THE INCREASED AIR NOISE IS DUE TO EXCESSIVE CLOGGING AT THE CABIN SIDEWALL DUCTING WHERE THERE IS A BAFFLE PLATE WITH HOLES TO FURTHER REDUCE THE AIR FLOW PRESSURE TO THE INDIVIDUAL SEAT ROWS. THIS BAFFLE HAS BEEN FOUND TO BE CLOGGED WITH LINT; DUST; HAIR AND DEBRIS. REPORTER BELIEVES THIS IS A HEALTH CONCERN. THIS BLOCKAGE THEN BACKS UP THE AIR FLOW AND PRESSURE INTO THE CENTER OVERHEAD DISTRIBUTION DUCT; CREATING HIGHER PRESSURE AND NOISE TO OTHER SEAT ROW DUCTS THAT ARE NOT BLOCKED AT THEIR BAFFLE PLATE. REPORTER STATED THEY HAVE TO USE FLEXIBLE BORESCOPE EQUIPMENT TO SEE AND WEAVE THEIR WAY DOWN INTO THE CABIN SIDEWALL DUCTING WHILE USING A VACUUM HOSE TO REMOVE THE ACCUMULATED DEBRIS FROM THE BAFFLE AT EACH SEAT ROW SIDEWALL.