B737-300 HAD A FALSE APU FIRE WARNING AT THE GATE. APU WAS SHUT DOWN AND ACFT DEPARTED WITH APU SHUT DOWN. DEFERRAL WAS NOT OBTAINED FROM MAINT. LATER; DURING TKOF; ANOTHER FALSE WARNING WAS RECEIVED. TKOF ABORTED AND RETURNED TO THE GATE. A PINCHED WIRE WAS FOUND IN THE FIRE WARNING CIRCUIT.

Narrative

AFTER PUSHBACK DURING #1 ENG START WE GOT APU DETECTION INOP LIGHT ON. SHUT DOWN APU -- CHKED IRREGULAR PROC. NOTIFIED PSP OPS TOLD THEM TO CONTACT MAINT. I HAD FLOWN INTO PSP BEFORE AND I KNEW I COULDN'T REACH MAINT THROUGH COMMERCIAL RADIO ON GND. I TOLD OPS WE'D CONTACT MAINT AIRBORNE. WE STARTED #2 ENG THROUGH XBLEED. TAXIED OUT; COMPLETED CHKLIST. ON TKOF ROLL; APPROX 80 KTS WE GOT AN APU FIRE WARNING (FIRE BELL AND LIGHT IN HANDLE). CAPT ABORTED TKOF. FO PULLED APU FIRE HANDLE AND SHOT FIRE BOTTLE. NOTIFIED TWR OF ABORT AND CALLED FOR FIRE TRUCKS. BOTH TWR AND FIRE CREWS RPTED NO SMOKE OR VISIBLE FIRE. RETURN ACFT TO GATE -- DEPLANED PEOPLE; NOTIFIED MAINT; DISPATCH THROUGH OPS TELEPHONE. MECH FOUND APU DETECTION WIRE PINCHED -- GIVING FALSE WARNING. CLRED ACFT THROUGH MAINT TO CONTINUE TO DEN WITH APU INOP. ON REVIEWING INCIDENT; I SHOULD HAVE WAITED ON GND TO GET MAINT CLRNC WITH APU INOP. PROB IS CREWS NORMALLY SHUT DOWN APU AFTER ENG START; AS A HABIT. HOWEVER; WITH APU DETECTION INOP; WE NEEDED MAINT CLRNC. I KNEW I COULD NOT REACH MAINT THROUGH COMMERCIAL RADIO BUT I SHOULD HAVE USED OTHER METHODS. (IE; WAITED FOR OPS TO RELAY.) TRYING TO KEEP ON SCHEDULE WAS ALSO A FACTOR.