AN ACR HAS A PRESSURIZATION LOSS DURING DSCNT. CTL OF CABIN ALT IS REGAINED WITH PROVIDED MANUAL CTL PROC.

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WE EXPERIENCED A SLOW LOSS OF PRESSURIZATION AS WE WERE DSNDING OUT OF FL350. THE FIRST INDICATION WAS A FLOW LIGHT ILLUMINATION; AND AT THE TIME; SINCE WE WERE IN THE CLR; WE DID NOT HAVE ANTI-ICE ON. (THE PRESSURE OUTPUT ON BOTH PACKS APPEARED WITHIN THE NORMAL RANGE AT THE TIME.) AT FIRST GLANCE THE OUTFLOW VALVE APPEARED TO BE CLOSED; BUT THE CABIN RATE OF CLB WAS OVER 1500 FPM CLB. AT THE TIME WE WERE DSNDING TO FL240. EVEN THOUGH THE CABIN ALT INDICATOR WAS RISING SLOWLY; I DECIDED IT WOULD BE BEST TO WEAR OUR OXYGEN MASKS; AND TOLD FO TO TELL ATC WE WERE HAVING TROUBLE HOLDING OUR CABIN PRESSURE AND WE NEEDED A CLRNC TO 14000 FT. I INSTRUCTED THE FO TO FOLLOW THE 'CABIN ALT WARNING/RAPID DEPRESSURIZATION' PROC WHILE I FLEW THE AIRPLANE. DURING THIS TIME WE RECEIVED CLRNC TO DSND TO 14000 FT. SINCE THE CABIN WAS DEPRESSURIZING SLOWLY; AND ATC HAD GIVEN US OUR DESIRED ALT; I CHOSE NOT TO DECLARE AN EMER. BY THE TIME WE WERE PASSING FL230; THE FO WAS TRYING TO MANUALLY CTL THE PRESSURE IN ACCORDANCE TO THE PROC; SINCE JUST PRIOR TO THAT TIME THE AUTOMATIC SYS HAD THE OUTFLOW VALVE PARTIALLY OPEN. HE COULD NOT GET THE CABIN TO DSND. I FELT HE WAS A LITTLE SLOW IN GETTING THE PROC COMPLETED. DURING THE DSCNT THE CABIN ROSE TO SLIGHTLY ABOVE 11000 FT AND I WAS ABLE TO GET THE AIRPLANE DOWN FAST ENOUGH TO AVOID THE DEPLOYMENT OF THE PAX OXYGEN MASKS. DURING THE DSCNT I ADVISED THE FLT ATTENDANTS TO BE PREPARED TO WEAR OXYGEN; BECAUSE WE WERE LOSING PRESSURIZATION. WE DSNDED FURTHER TO 10000 FT. AT BTWN 14000 FT AND 10000 FT ACFT ALT; THE FO REGAINED CTL OF THE CABIN PRESSURE MANUALLY AND WAS ABLE TO BEGIN A SLOW DSCNT OF THE CABIN ALT. THE REMAINDER OF THE FLT WAS UNEVENTFUL. EXTRA NOTE: AFTER WE LEVELED OFF I NOTICED HE DID NOT MANUALLY COMPLETELY CLOSE THE OUTFLOW VALVE. WE STARTED GETTING PRESSURE BACK AFTER HE FIGURED THE CTL OUT.