AN MD80 FLT CREW EXPERIENCED A CABIN ALT WARNING LIGHT AND EXCESSIVE CABIN ALT. THEY DECLARED AN EMERGENCY AND EXECUTED AN EMERGENCY DESCENT; REGAINING NORMAL PACK OPERATION AT 10000 FT.

Narrative

TAXI/TKOF/CLB UNEVENTFUL. PASSING THROUGH 17000 FT; RECEIVED DIRECT TO ZZZ; TOOK A HDG CHANGE DUE TO TSTMS. CHKED PRESSURIZATION ON CLB CHK -- READ PROPERLY. GOING IN AND OUT OF CLOUDS AND NOTICED RAM AIR TEMP AT 5 DEGS C AROUND FL200. PUT ON ENG AND WING ANTI-ICE. CHKED WX RADAR AND GETTING NAV SET UP FOR DIRECT MLC WHEN CABIN ALT WARNING LIGHT CAME ON AT FL300. CHKED PACKS -- BOTH ON WITH LOW FLOW. CABIN ALT READ 9000 FT; CABIN READ 300 FT RISE. NO ICING NOTED ON WIPER BLADE PIN. HAD NO PRESSURIZATION FLOW LIGHT OR ANY OTHER LIGHTS. REQUESTED DSCNT FROM CTR. STARTED DSCNT TO FL240; THEN CTR GAVE US FL190. DECLARED AN EMER AND ACCOMPLISHED THE IMMEDIATE ACTION ITEMS. CABIN ALT ROSE TO 11500 FT. PRESSURE STOPPED RISING AFTER ACCOMPLISHING IMMEDIATE ACTION ITEMS. ACCOMPLISHED REST OF THE CHKLIST EXCEPT FOR DEPLOYING THE PAX'S MASKS (ALT BELOW 14000 FT WITH CABIN READING 7000 FT BY THIS TIME). PACKS STARTED WORKING FINE AFTER LEVELING OFF AT 10000 FT. CAPT GAVE ME THE ACFT SINCE HE HAD AN EAR BLOCK. LANDED AT ZZZ WITHOUT INCIDENT. TAXIED TO GATE AND DEBRIEFED MAINT PERSONNEL. ACFT TAKEN OTS. ALL 3 FLT ATTENDANTS AND I WERE FINE. CAPT HAD TO TAKE HIMSELF OFF THE TRIP DUE TO HIS EAR.