TWO LINE MECHANICS; TROUBLESHOOTING A B757-200 ACFT WITH A LENGTHY HISTORY OF LEFT RECIRC FAN OVERHEAT WARNING HORN NOT SOUNDING; NOTICE THE CONNECTOR WIRE FOR THE HORN WAS NOT REINSTALLED. THIS IS AN MEL ISSUE.

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I WAS ASSIGNED ACFT X THAT HAD A LENGTHY HISTORY OF LEFT RECIRC FAN NO OVERHEAT WARNING HORN SOUNDING. THE WRITE UP WAS TO CHECK THAT THE WIRE PULLED IN THE MEL WAS INSTALLED. IT WAS NOT INSTALLED. I SPOKE WITH LINE MAINT CONTROL AND WAS TOLD THAT THIS WAS POSSIBLY AN ISOLATED PROBLEM. THE NEXT NIGHT I DID A SPOT CHECK ON MY OWN AND FOUND 1 OUT OF 3 B-757'S THAT DID NOT WORK. THAT IS 33 PERCENT; NOT GOOD. I HAPPEN TO SPEAK WITH MY COWORKER ABOUT THIS ISSUE AND FOUND OUT THAT THIS HAS BEEN HAPPENING FOR THE LAST 4 YEARS. THIS HAS LED ME TO BE CONCERNED; AND YES THERE ARE STILL PEOPLE AT OUR ACR THAT ARE SERIOUS ABOUT THEIR JOBS. SO I THINK THAT THIS ITEM NEEDS MORE ATTENTIONSUPPLEMENTAL INFO FROM ACN 786542: FOR APPROX 4 YEARS NOW THERE HAS BEEN AN ONGOING PROBLEM WITH THE REACTIVATION PROCEDURE FOR THE LEFT RECIRC FAN ON THE B757. THE MEL REQUIRES THE REMOVAL OF WIRE.CALLBACK CONVERSATION WITH RPTR 786543 REVEALED THE FOLLOWING INFO: REPORTER STATED MEL CHAPTER 21 ALLOWS FOR DEFERRAL OF THE LEFT RECIRC FAN AS INOP ON THE B757-200 ACFT; WITH THE PROVISO THAT THE ELECTRICAL WIRE FOR THE RECIRC FAN WARNING HORN BE PULLED FROM THE CANON PLUG CONNECTOR AND THE LEFT RECIRC FAN OVERHEAD SWITCH BE PLACED IN THE 'OFF' POSITION. REMOVING THIS WIRE FROM THE CONNECTOR PREVENTS THE RECIRC FAN WARNING HORN FROM CONSTANTLY SOUNDING WHEN THE LEFT RECIRC FAN IS NOT FUNCTIONING; OR; AS IN THIS CASE; WHEN THE FAN SWITCH IS PLACED IN THE 'OFF' POSITION. REPORTER STATED THE PROBLEMS APPEAR TO BEGIN WHEN THE FAN IS REPLACED AND THE FAN SWITCH IS PLACED IN THE 'ON' POSITION TO CHECK FOR FAN OPERATION. THE MEL PROCEDURE DOES NOT REFERENCE MAINT MANUAL CHAPTER 32; WHICH IS ANOTHER PROCEDURE TO VERIFY THE WARNING HORN SOUNDING APPROX 30 SECONDS AFTER THE LEFT RECIRC FAN SWITCH IS PLACED IN THE OFF POSITION. IF MECHANIC ONLY FOLLOWS THE MEL CHAPTER 21 PROCEDURE AFTER REPLACING THE RECIRC FAN; AND SIGNS-OFF THE WRITE-UP; CLEARING THE MEL; AND DOES NOT GO TO THE MM CHAPTER 32; THEN ACFT COULD BE AND HAVE BEEN RELEASED WITHOUT THE WARNING HORN BEING FUNCTIONAL. THIS WAS CAUSED BY THE ELECTRICAL WIRE FOR THE FAN WARNING HORN NOT BEING REINSTALLED INTO THE CONNECTOR. REPORTER ALSO STATED HIS CARRIER'S MAINT CONTROL AND ENGINEERING HAVE DONE VERY LITTLE IN ADDRESSING THIS ISSUE.