F100 CREW HAD LOW APU PNEUMATIC PRESSURE DURING ENG START.

Narrative

APU LOST PRESSURE OUTPUT. ARRIVED AT THE ACFT; CHKED THE LOGBOOK -- CLEAN. COMPLETED CHKLIST; PREPARED FOR A START TO PWRBACK. ATTEMPTED TO START #1. DUE TO LOW PRESSURE; ABORTED START. COPLT ASKED IF I WANTED TO CALL MAINT. I SAID 'NO; ASK FOR A TART CART.' I CONSIDERED THAT REASONABLE DUE TO THE WARM GUSTY CONDITIONS. DUE TO THE POSITION OF THE ACFT; THERE WAS ALSO A TAILWIND. HOOKED UP THE START CART; STARTED ENGS AND LEFT. WRONG DECISION. ARRIVED AT OMA; STARTED THE APU; THEN NOTICED THE PRESSURE ONCE AGAIN LOWER THAN NORMAL. TURNED OFF THE PACKS. PRESSURE APPEARED TO BE NORMAL AROUND 44 PSI. I ELECTED TO CALL MAINT AS I WAS UNSURE AS TO THE INTEGRITY OF THE SYS. THE APU WAS PLACARDED BY CONTRACT MAINT. WE INCURRED A 2 1/2 HR DELAY DUE TO MY WRONG DECISION AT THE START. HAD WE CALLED MAINT IN DFW; SURE WE WOULD HAVE BEEN DELAYED MORE; BUT NOT AS LONG AS OUR DELAY IN OMA. I GUESS PART OF MY REASONING INCLUDED THAT WE WERE ALREADY 1 HR BEHIND DUE TO WX; DUE TO A DIFFERENT ACFT WITH SIMILAR PROBS. I GUESS; IN TRYING SO HARD NOT TO MAKE A WRONG DECISION; I MADE A WRONG DECISION.