What was found
NR 2 ENGINE A-FIRE DETECTION LOOP CAME ON STEADY IN CLIMB. SWITCHED TO B-LOOP AND TEST IAW OPS MANUAL CHECKED GOOD. APPROXIMATELY 5 MINUTES LATER FIRE WARNING SOUNDED ON B-LOOP, SHUT NR 2 ENGINE DOWN IAW OPS MANUAL. INSPECTED NR 2 ENGINE, NO DEFECTS FOUND. SWAPPED APU AND NR 2 ENGINE FIRE DETECTOR CONTROL UNITS FOR FURTHER TROUBLESHOOTING. APU FIRE DETECTION SWITCH CHECKS NORMAL AND PERFORMED HIGH POWER RUN ON NR 2 ENGINE, CHECKS NORMAL ON GROUND AT THIS TIME.