B737-300 CREW WAS NOT ABLE TO PRESSURIZE THE ACFT FOR A THIRD TIME.

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PREVIOUS 2 REVENUE FLTS ON THIS ACFT. INVOLVED INABILITY TO PRESSURIZE; DESPITE ATTEMPTS TO USE EACH OF THE 4 MODES OF THE PRESSURE CTLR TO ASSURE CLOSURE OF THE OUTFLOW VALVE (VALVE INDICATED CLOSED). WE RETURNED TO THE ARPT AND BOTH TIMES MAINT THOROUGHLY CHKED SYS AND RETURNED ACFT TO SVC WITH NO MALFUNCTIONS OBSERVED. (SECOND TIME I PERSONALLY WITNESSED THE MAINT TROUBLE-SHOOTING PROCS.) THEN WE WERE DIRECTED TO FERRY THE ACFT TO OUR MAINT BASE IF POSSIBLE. AGAIN; ON TKOF; WE WERE UNABLE TO PRESSURIZE VIA ANY PRESSURIZATION MODE SELECTION AS CALLED FOR IN OUR 'AUTO FAIL OR UNSCHEDULED PRESSURIZATION CHANGE' NON-NORMAL CHKLIST. WE THEN SELECTED THE HI MODE ON BOTH ACFT PACKS; THE ACFT PRESSURIZED; AND WE CONTINUED TO DEST. I FOUND OUT TODAY THAT MAINT REPLACED THE PRESSURE CTLR. TEST FLEW THE ACFT AND RETURNED IT TO REVENUE SVC. ALSO; TODAY I REVIEWED MY MANUAL AND SAW THAT THE 'CABIN ALT WARNING OR RAPID DECOMPRESSION/EMER DSCNT' CHKLIST CALLED FOR THE ADDITIONAL STEP OF PLACING THE LEFT AND RIGHT PACK SWITCHES TO HI. WE USED THE WRONG CHKLIST FOR THE SIT! (I AM JUST DISCOVERING THIS NOW -- THE LATE NASA RPT.) I FEEL SO BADLY ABOUT THIS -- THE INCONVENIENCE TO 2 PLANELOADS OF PAX; THE EXPENSE; AND INCONVENIENCE FOR MY COMPANY; BECAUSE WE DIDN'T USE PROPER PROCS. ALL INVOLVED ARE STILL STYMIED AS TO WHY THE ACFT COULD BE PRESSURIZED FULLY ON THE GND BY MAINT IN MEX; AND ALSO WHY CHANGING THE PRESSURE CTLR WOULD FIX THE PROB WHEN THE PREVIOUS ONE CHKED OUT PROPERLY BY MAINT PROCS. BOTTOM LINE FOR ME -- THE ACFT HAD A PROB; AND I HAD A CHANCE TO MITIGATE THAT PROB EXPEDITIOUSLY. YET DESPITE OUR CONCERTED BEST AIRCREW EFFORTS; WE BLEW IT. I'LL CERTAINLY MAKE EVERY EFFORT; MORE OF AN EFFORT; IN THE FUTURE; TO USE THE RIGHT CHKLIST.