LOSS OF CABIN PRESSURIZATION IN ACR ACFT CAUSES FLC TO DSND FROM FL230 TO 10000 FT MSL.

Narrative

DURING CLB AT FL230 1 BEEP WAS HEARD FROM A WARNING HORN. A RAPID SCAN OF THE COCKPIT DID NOT REVEAL ANY WARNING LIGHTS ON. ABOUT 5 SECONDS LATER THE CABIN ALT WARNING HORN CAME ON STEADILY. CABIN ALTIMETER WAS AT 10000 FT WITH A 3 PSI DIFFERENTIAL AND A 500-700 FPM CLB. CARGO HEAT OUTFLOW VALVE WAS CLOSED; ATC ADVISED AND A RAPID DSCNT WAS INITIATED TOWARD 10000 FT WHILE CONTINUING TO EVALUATE. RECYCLED PACK SWITCHES AND FOUND THAT THE R PACK HAD NOT BEEN PROVIDING ANY PRESSURE. AFTER RECYCLING; THE CABIN IMMEDIATELY BEGAN TO REPRESSURIZE. MAX CABIN ALT WAS ABOUT 10500 FT FOR LESS THAN 1 MIN. DSCNT WAS CONTINUED TO 10000 FT BECAUSE WE WERE NOT SURE WHAT HAD CAUSED THE PROB. LEVEL AT 10000 FT; WE CYCLED EACH PACK OFF INDIVIDUALLY AND FOUND THAT THE R PACK HELD CABIN PRESSURE FINE; BUT THE L PACK COULD NOT. DISPATCH AND MAINT WERE CONTACTED AND ADVISED OF SIT. WRITE-UPS WERE ENTERED IN THE LOGBOOK FOR LOSS OF CABIN PRESSURE; USE OF THE OXYGEN BOTTLE AND RESULTS OF TROUBLESHOOTING THE PACK SYS.