RETURN LAND MANDATED FOR THE FLT CREW OF A B737-700 WHEN THEY ARE UNABLE TO PRESSURIZE THE ACFT THROUGH NORMAL AND ALTERNATE PROCS AFTER TKOF FROM ANC; AK.

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CLBING THROUGH 10000 FT; THE ALT WARNING HORN SOUNDED. FO LEVELED OFF AND IMMEDIATELY NOTICED THAT THE PRESSURIZATION CTLR WAS IN 'MANUAL.' HE SELECTED 'AUTO' AND WE OBSERVED OUTFLOW VALVE WHILE CONTACTING ATC OF OUR LEVELOFF. OUTFLOW VALVE REMAINED IN FULL OPEN POS IN BOTH 'AUTO' AND 'ALTERNATE.' AFTER GETTING 180 DEG VECTOR; IT BECAME OBVIOUS THAT CABIN WOULD NOT PRESSURIZE. WE REQUESTED A LONG SLOW DSCNT FOR PAX COMFORT AND LANDED ANC UNEVENTFULLY. MAINT WAS ABLE TO CYCLE THE VALVE AND SYS WAS CHKED AND RELEASED. OVERWT LNDG INSPECTION COMPLETED. REDISPATCHED FLT UNEVENTFUL. THE MANUAL SWITCH POS WAS MISSED DURING BOTH OUR PREFLTS; HOWEVER THE OUTFLOW VALVE DID MALFUNCTION; AS NORMAL CABIN PRESSURIZATION SHOULD HAVE BEEN AVAILABLE UPON SELECTION OF 'AUTO.' THE SIGNIFICANCE OF THIS EVENT LIES IN A SEEMINGLY INCONSEQUENTIAL OVERSIGHT. PREFLT WAS DONE IN EARLY DAWN LIGHT WITH THE COCKPIT LIGHT SELECTOR IN 'DIM.' WITH THE RISING SUN IN OUR EYES; WE DID NOT SELECT 'BRIGHT.' THIS PREVENTED ME FROM 'TRAPPING AND MITIGATING' THE ORIGINAL MISTAKE DURING MY AFTER TKOF CHK OF BLEEDS AND PACKS; BY NOT NOTICING THE GREEN 'MANUAL' LIGHT ON THE AC PANEL. WE CONFIRMED THAT IN 'DIM;' THE LIGHT IS INVISIBLE IN A BRIGHTLY LIT COCKPIT. I WILL BE MORE COGNIZANT OF THE AC PANEL DURING PREFLT AND CERTAINLY BE MORE CAREFUL OF THE LIGHT POS SWITCH AS CONDITIONS CHANGE. SUPPLEMENTAL INFO FROM ACN 611570: DURING PREFLT ON A B737-700; I NOTICED THE PRESSURIZATION OUTFLOW DOOR WAS OPEN. THE OAT WAS ABOUT -7 DEGS C; SO I ASSUMED MAINT HAD NOT CLOSED THE DOOR AS THEY USUALLY DO WHEN THE ACFT REMAINS OUT OVERNIGHT. I WAS INFORMED; LATER; THEIR PROC IS TO LEAVE IT OPEN WHEN WARM AIR IS SUPPLIED TO THE ACFT (MY ONLY QUESTION WOULD BE: WHY THEY DID NOT RE-SELECT AUTO). WHEN DOING THE COCKPIT PREFLT; I MISSED THE PRESSURIZATION CTL ROTARY SWITCH WAS IN 'MANUAL;' RATHER THAN 'AUTO.' IT WAS MISSED DURING THE BEFORE START CHK AND ON THE AFTER TKOF CHK. ALSO; NEITHER THE AUTO FAIL LIGHT NOR THE ALTERNATE WOULD COME ON WHEN SELECTED.