A B737-700 LOST CABIN PRESSURIZATION AT FL390. CREW SELECTION OF ALTERNATE MODE REGAINED CTL. EMER DECLARED WITH DSCNT TO 14000 FT.

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RAPID DECOMPRESSION AT FL390; NO WARNING HORN; NO AUTO FAIL LIGHT; NO MASTER CAUTION; NOTHING PRIOR TO THE CABIN DEPRESSURIZING. FIRST INDICATION WAS PRESSURE CHANGE IN YOUR EARS IMMEDIATELY FOLLOWED BY CABIN WARNING HORN AND THE DROPPING OF ALL THE MASKS. CABIN WENT TO 15000 FT IN A MATTER OF SECONDS. WHEN I FELT THE PRESSURE CHANGE; IMMEDIATELY I LOOKED UP AND SAW THE CABIN RATE OF CLB INDICATOR AT MAX RATE; AND 15000 FT SHOWING ON THE CABIN ALT INDICATOR. SWITCHING RIGHT AWAY TO ALTERNATE MODE; CLOSED THE OUTFLOW VALVE; AND STOPPED THE CABIN FROM CLBING ANY FURTHER. THEN; TRYING TO PUT ON THE OXYGEN MASK; IT KNOCKED OUT MY EARPIECE AND I WAS UNABLE TO HEAR IF WE HAD BEEN CLRED TO DSND. I QUESTIONED THE FO IF WE HAD OUR DSCNT CLRNC; BUT HE HAD EXPERIENCED THE SAME PROB; LOSING HIS EARPIECE. THE OXYGEN MASK SEEMS LIKE A SIMPLE PROC; AND IT SHOULD BE; BUT IT WAS THE MOST DIFFICULT PART OF THE QRH. FINALLY; WE HAD OUR MASKS ON; COMMUNICATIONS ESTABLISHED; AND BEGINNING OUR DSCNT TO 14000 FT. THE FO RAN THE QRH; RAPID DECOMPRESSION CHKLIST; CLOSING THE OUTFLOW VALVE MANUALLY; ETC. AS WE WERE DSNDING; WE NOW NOTICED THE CABIN WAS ACTUALLY OVER PRESSURIZING. THE CABIN ALT INDICATOR WAS SHOWING JUST OVER 2000 FT WITH A PRESSURE ALT OF 30000 FT. SWITCHING BACK TO ALT MODE CORRECTED THE PROB. THE QRH I KNOW SAYS TO CTL THE CABIN IN MANUAL MODE BUT AT NIGHT IN THE DARK; IT'S A LITTLE HARD TO READ AND THERE'S A LOT GOING ON. MAYBE IF IT WAS IN BOLDER PRINT IT WOULD HELP. ALSO; PERHAPS THE FIRST OPTION MIGHT BE TO SWITCH TO ALT MODE. IF THIS CTLS THE PRESSURIZATION; JUST LEAVE IT THERE. WHEN I FIRST SWITCHED TO ALTERNATE; IT SOLVED THE PROB; BUT THEN GOING THROUGH THE CHKLIST WE CREATED ANOTHER PROB BY SWITCHING TO MANUAL. JUST SOMETHING TO CONSIDER. WITH THE CABIN AT A NORMAL DIFFERENTIAL THE DSCNT WAS REDUCED TO A MORE NORMAL RATE UNTIL LEVELING AT 14000 FT. WITH NO STRUCTURAL DAMAGE; NO PAX ISSUES; ARR FUEL TO DEST SHOWING 6000 LBS AND EVERYTHING OPERATING NORMALLY; AFTER CONFERRING WITH DISPATCH THE DECISION WAS MADE TO CONTINUE ON TO ZZZ1. NO FURTHER PROBS WERE ENCOUNTERED. FLT ATTENDANTS WERE KEPT INFORMED AS MUCH AS POSSIBLE CONCERNING THE SIT. THEY DID A GREAT JOB OF KEEPING THE PAX CALM AND INFORMED. WE COMMUNICATED AS MUCH AS POSSIBLE VIA THE PA WITH THE PAX AS WELL AS THE FLT ATTENDANTS. OVERALL A GREAT JOB FOR EVERYONE INVOLVED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THE PRESSURE CTLR SHOULD HAVE AUTO SWITCHED TO ALTERNATE. THIS MODEL ACFT (B737-700) IS DIFFERENT FROM EARLIER MODELS IN THAT IT HAS TWO CTLRS (PRIMARY AND ALTERNATE); TWO NORMAL AC OUTFLOW VALVE MOTORS; AND A MANUAL CTLR AS WELL AS A MANUALLY CTLED MOTOR. WHEN THE CREW NOTICED THE PRESSURE CHANGE; THE CABIN LOST PRESSURE SO RAPIDLY THAT THE CABIN ALT WARNING SOUNDED AND EVEN AS ALTERNATE WAS SELECTED; THE CABIN CONTINUED TO 15000 FT BEFORE STABILIZING AND STARTING BACK DOWN. THE RPTR STATED THAT THE DAY PRIOR; THIS ACFT HAD EXACTLY THE SAME PROB BUT IT COULD NOT BE DUPLICATED ON THE GND AND SO NO ACTION WAS TAKEN. WITH THIS SECOND OCCURRENCE; TROUBLESHOOTING DIAGNOSED NO PROBS AGAIN SO THE ACR MAINT CHANGED THE PRESSURE CTLRS; THE COMPUTERS AND BOTH OUTFLOW VALVE MOTORS. THE MOST TROUBLING PROB FOR THE RPTR WAS THE OXYGEN MASK HARNESS KNOCKING THE EARPIECE OUT OF HIS EAR SO THAT HE COULD NOT HEAR ATC'S RESPONSE TO HIS DSCNT CLRNC.