ACR B737-700 DEPARTS BOG. FO INADVERTENTLY UNPRESSURIZED FOLLOWED BY APCH TO INCORRECT RWY AND OVERWT LNDG.

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RETURN TO ARPT (BOG) FOR OVERWT LNDG DUE TO A PRESSURIZATION PROB. BOG IS AN FAA SPECIAL ARPT WHICH REQUIRES SPECIAL ARR AND DEP PROCS FOR NORMAL AND ENG FAILURE. ARPT ELEVATION IS 8300 FT MSL WITH HIGH MOUNTAINOUS TERRAIN IN ALL QUADRANTS. WE TOOK OFF ON RWY 13R WHICH RECOMMENDS 'ICAO A' DEP PROCS FOR NOISE ABATEMENT. THIS REQUIRES PWR REDUCTION AT 1500 FT AGL (9800 FT MSL) AND CLEANUP AT 3000 FT AGL (11300 FT MSL). IT ALSO REQUIRES MAX ANGLE OF CLB TO 13000 FT MSL. DUE TO TKOF WT THIS TKOF REQUIRED A 'BLEEDS-OFF' CONFIGN. GRID MORA IN THE DEP TRACK WAS 14400 FT MSL. WE HELD FOR LNDG TFC ON RWY 13R AS WELL AS ON THE RWY FOR AN EXTENDED PERIOD. I PERFORMED THE TKOF CHK AND CONFIRMED CHKLIST COMPLETE; TO INCLUDE AIR CONDITIONING AND PRESSURIZATION CONFIGN. I WAS CONCERNED ABOUT THE PAX COMFORT AND THOUGHT ABOUT TURNING THE BLEED AIR SWITCHES ON TO IMPROVE AIR CONDITIONING (SO I THOUGHT). AFTER WE WERE CLRED FOR TKOF; THINKING THE BLEED AIR SWITCHES WERE ON; I REACHED UP TO TURN OFF THE BLEED AIR SWITCHES; BUT IN ACTUALITY THE BLEED AIR SWITCHES WERE OFF AND I TURNED OFF THE PACK SWITCHES. IT WAS MY TKOF AND I ASSUMED CTL OF THE ACFT AND BEGAN THE TKOF. TKOF WAS NORMAL. OUR FIRST ATTEMPT TO BOG DEP WAS UNANSWERED AND THEY ANSWERED OUR SECOND CALL. THE CABIN ALT HORN WENT OFF AS I WAS IN A R TURN AT ABOUT 11000 FT MSL. THE CAPT SILENCED THE HORN AND I VERIFIED THAT THE CABIN ALT WAS CLBING. HE ASKED THAT I LEVEL OFF AS WE WERE PASSING ABOUT 12000 FT MSL BUT DUE TO A HIGH TERRAIN AND THINKING 14400 FT MSL (GRID MORA) WOULD BE A SAFE ALT. I CALLED FOR FLAP RETRACTION AT 12500 FT MSL AND AN AFTER TKOF CHKLIST. THE CAPT TURNED THE PACK SWITCHES TO HIGH AND VERIFIED THE CABIN WAS PRESSURIZING BUT THE PAX MASKS ALREADY DEPLOYED SO WE RETURNED TO BOG. THE CAPT REQUESTED A RETURN TO BOG FOR APCH; HE DIRECTED ME TO FLY THE ACFT AS HE COMPLETED THE CHKLIST. WE WERE CLRED DIRECT TO BOG VOR AND CLRED FOR ILS APCH. WE INADVERTENTLY TUNED-IN THE RWY 13L ILS VICE RWY 13R WHICH THE TWR RECOGNIZED AND ASKED US TO TRANSITION TO RWY 13R. ONCE ESTABLISHED RWY 13R ILS APCH AND LNDG WERE NORMAL. THE CAPT TOOK CTL OF THE ACFT AT 1000 FT AGL AND ACCOMPLISHED THE LNDG. MY FIRST PRIORITY ON DEP WAS TO HIT THE GND; SO I ASSUMED THE CAPT WANTED ME LEVEL OFF AT AN ACCEPTABLE TERRAIN CLRNC ALT. SINCE WE WERE FLYING AN LNAV DEP AND THE CAPT WAS PREOCCUPIED WITH THE PRESSURIZATION PROB; I THOUGHT THE GRID MORA (14400 FT MSL) WAS THE SAFEST ALT. MY LESSON LEARNED IS TO VERIFY THE AIR CONDITIONING AND PRESSURIZATION SWITCHES WITH THE OTHER PLT BEFORE TKOF. I WILL NOT CHANGE ANY SWITCHES AFTER A CHKLIST IS COMPLETE; UNLESS VERIFIED BY THE OTHER PLT. WE ALSO SHOULD HAVE HELD AT BOG VOR TO PROVIDE MORE TIME FOR RECOVERY.