A B737-300 IN CLB AT FL230 DECLARED AN EMER AND DIVERTED DUE TO LOSS OF CABIN PRESSURE CAUSED BY INCORRECT ENG BLEED CONFIGN.

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WE DID AN XA30 DEP FROM MEXICO AT A WT OF 120000 LBS AND DID AN IMPROVED BLEEDS OFF TKOF. MAX DEP IS A LITTLE DIFFERENT BECAUSE YOU CLB AT 180 KTS FOR 5 MI WHICH MAKES NORMAL INITIAL CLB AND PROCS HAPPEN LATER THAN NORMAL. AT APPROX 10500 FT I WAS STILL HAND FLYING THE ACFT AND HAD THE FO DO THE AFTER TKOF CHKLIST; WHICH SHOULD INCLUDE RESETTING THE APU BLEED OFF AND ENG BLEEDS BACK ON FOR NORMAL PRESSURIZATION TO VERIFY THE CABIN IS PRESSURIZED PROPERLY. AT THAT TIME HE (FO) POINTED OUT THE CABIN WAS DSNDING TO THE PROPER CABIN ALT (MAX IS 7300) CONTINUING WITH THE REST OF THE CHKLIST. WE PROCEEDED ON THE LUCIA TRANSITION AS PER THE SID. AFTER PASSING LUCIA AT APPROX FL230; WE HEARD THE TKOF WARNING HORN GO OFF. BUT IN THIS CASE; IT'S THE SAME HORN USED FOR HIGH CABIN ALT 10000 FT. AT FIRST WE DIDN'T RECOGNIZE IT FOR WHAT IT WAS. THE FO LOOKED UP AND SAW THE CABIN WAS CLBING AT A VERY HIGH RATE; 2000-3000 FPM. I THEN SAID 'MASKS ON.' I GOT MINE ON FIRST AND SIMULTANEOUSLY PULLED THE SPD BRAKE OUT; STARTED THE DSCNT; AND TOLD ATC WE WERE 'COMING DOWN' LOSS OF PRESSURIZATION AND DECLARED AN EMER. THE OUTFLOW VALVE WAS CLOSED BUT WE WENT TO MANUAL ANYWAY. I TOLD THE FO TO TELL THE FLT ATTENDANTS OVER THE PA WE'RE ON AN EMER DSCNT AND TO SIT DOWN. THE CABIN SIGN WAS ON AND THE ONLY THING WE DID DO WAS SQUAWK 7700. IT WAS A VERY STRESSFUL AND BUSY TIME. I CONTINUED TO FLY THE ACFT. WE WERE GETTING VECTORED TO MATEO (SMO). THE CDU WOULDN'T TAKE IT BECAUSE THERE ARE 2 SMO'S IN THE BOX AND WITH UPDATE 1.6 YOU CANNOT LINE SELECT IT DOWN THEN GO TO THE LEGS PAGE. THE FO WAS STRESSED AND IT TOOK HIM A LONG TIME TO COME UP WITH THE VOR FREQ FOR ME; SO FOR A WHILE I DIDN'T KNOW EXACTLY WHERE I WAS AND THAT BOTHERED ME. WE RETURNED FOR AN OVERWT LNDG. POSTFLT INSPECTION FOUND THE ACFT PRESSURIZATION WORKS FINE; NO PROB WITH THE OVERWT LNDG. EXPECTED CAUSE OF LOSS OF PRESSURIZATION WAS THE FO FAILED TO DO PROPER TKOF CHK BY NOT RESETTING THE ENG DRIVEN BLEEDS BACK TO NORMAL. OUR LOSS OF PRESSURIZATION CHKLIST SAYS MASKS ON; ESTABLISH COM SELECTION TO MANUAL; CLOSE THE OUTFLOW VALVE; IF PRESSURIZATION CANNOT BE MAINTAINED; DO AN EMER DSCNT. IT NEVER SAYS CHK THE BLEEDS OR PACKS.