What was found
PHX - AIR TURNBACK - 2/25/01 - DURING CLIMB AT 18,000 FT THE CREW PERFORMED AN ENGINE FIRE WARNING TEST; NEITHER ENGINE WOULD TEST PLUS THE FAULT LIGHT WAS ON. THE AIRCRAFT RETURNED TO PHX. ON GROUND THE ENGINE FIRE TEST WAS NORMAL; THE NR 1 ENG FIRE LOOP B HAD BEEN PLACED ON MEL 26-2 ON THE PREVIOUS FLIGHT. IN PHX MAINTENANCE RANG OUT THE WIRING FROM THE FIRE CONTROL MODULE TO THE FIRE PROTECTION BOX AND ALL CHECKS WERE GOOD. REMOVED AND TESTED NR 1 ENG STRUT DETECTOR ASSY AND FIRE DETECTOR ASSY, TESTED GOOD. BOTH WERE REPLACED AS PRECAUTION AND FUNCTIONAL TESTS WERE GOOD. DETECTOR ASSY P/N 472094 - LOCATION: NR 1 ENGINE.