B737-300 FLT CREW HAS MAINT ISSUE WITH ACFT AND REQUESTS DISPATCH SUPPLY ANOTHER ACFT FOR THE REMAINING LEGS OF THE FLT.

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DEPARTING FLT SCHEDULED OUT OF PHX. ACFT LATE INBOUND DUE TO MAINT PROBS ON PREVIOUS FLT. CAPT DEBRIEFED ME AS FOLLOWS: COULD NOT GET #1 GENERATOR ON LINE AFTER PUSHBACK. WENT BACK TO GATE TO CALL CONTRACT MAINT. GOT GENERATOR ON LINE; BUT FOUND ACFT TO HAVE A HISTORY OF TROUBLE WITH #1 GENERATOR. ON TKOF; BOTH ENGS OVERTEMPED WITH ACCOMPANYING RED LIGHT IN EGT INSTS. LATER FINDS OUT ACFT HAS ALSO HAD A HISTORY OF OVERTEMP EXCEEDANCES (3 TIMES FOR #1 ENG; 4 TIMES FOR #2 ENG). TEMP AT ELP FOR TKOF WAS 33 DEGS C. AFTER CONFERRING WITH MAINT; I CHOSE TO REFUSE ACFT WITH A PHX TKOF TEMP OF 38 DEGS C AND THE ACFT'S PREVIOUS HISTORY. I PROMPTLY TOLD DISPATCH AND SHE SAID OK. I THEN RECEIVED A NEW RELEASE WITH A NEW ACFT. MAINT SUBSEQUENTLY MOVED ACFT OFF GATE; ONLY TO HAVE IT RETURN TO GATE APPROX 15 MINS LATER; AND I WAS TOLD DISPATCH DID NOT WANT TO SWAP ACFT (TRYING TO OVERRIDE MY DECISION NOT TO ACCEPT ACFT -- AS I SEE IT). ALL OF THIS IS GOING ON IN PLAIN VIEW OF OUR PAX; WHO WERE EVIDENTLY TOLD BY THE OPS AGENT THAT THE ACFT HAD A MAINT PROB AND THAT WE WOULD BE GETTING ANOTHER ACFT FOR OUR FLT. I FELT VERY SECURE IN MAKING THIS DECISION TO REFUSE THE ACFT FOR SAFETY REASONS. IT TURNS OUT THAT WE HAD TO USE MAX PWR FOR TKOF WHEN WE FINALLY DEPARTED SMF (MODERATELY HVY FUEL LOAD AND APPROX 100 PAX). IT WAS CLR TO ME THAT BOTH ENGS WOULD AGAIN HAVE OVERTEMPED UNDER THE CONDITIONS IN PHX (38 DEGS C). WHEN I AGAIN TOLD DISPATCH THAT I REFUSED TO TAKE THAT ACFT; SHE INITIATED A CONFERENCE CALL WITH THE CHIEF PLT ON DUTY; SUPVR OF DISPATCH; MY DISPATCHER AND MYSELF. CHIEF PLT ON DUTY AFTER LISTENING TO THE FACTS; TOLD THE DISPATCHER THAT 'HE TENDED TO AGREE WITH THE CAPT.' I WAS DROPPED FROM THE CONFERENCE CALL SO THEY COULD DISCUSS THE ISSUE FURTHER. EVENTUALLY (1 HR 45 MINS AFTER THE PREVIOUS ACFT BLOCKED IN) WE GOT ANOTHER ACFT AND CONTINUED THE TRIP (2 MORE LEGS).