MD80 WAS DISPATCHED WITH ONE PACK INOP. REMAINING PACK SHUT DOWN; AND FLT CREW DECLARED EMER WHILE TROUBLESHOOTING ANOMALY.

Narrative

WE DEPARTED WITH 1 PACK INOP. CLBING OUT I SELECTED THE CABIN TEMP TO WARMER AND THE TEMP CTL VALVE WAS NOT RESPONDING IN THE AUTO POS. SINCE THE PREVIOUS FLT COMPLAINED THAT THE CABIN WAS COLD; I WANTED TO TRY TO KEEP THE CABIN COMFORTABLE ON THIS LEG. I SELECTED MANUAL TO DRIVE THE TEMP VALVE OFF OF COLD TO START WARMING THE CABIN. I POSITIONED THE VALVE ABOUT THE NORMAL 10 O'CLOCK POS. I WAS THEN DISTR BY OTHER DUTIES AND DID NOT PUT THE AIR CONDITIONING CTL BACK TO AUTO. CAPT NOTICED IT WAS GETTING HOT IN THE COCKPIT AND WE LOOKED UP TO SEE WHAT THE PROB WAS. WE NOTICE A HIGH SUPPLY TEMP AND HIGH RATE OF CLB IN THE CABIN. WE ALSO HAD A PRESSURIZATION FLOW ANNUNCIATOR. THE OPERATING PACK HAD SHUT DOWN. I BELIEVE THE CABIN WAS ONLY ABOUT 4000 FT AT THIS TIME. WE DECLARED AN EMER AND DSNDED TO A LOWER ALT. DURING THIS TIME THE PACK CAME BACK ON AND FLOW RETURNED TO NORMAL. I SELECTED AUTO AND COOLER ON THE TEMP CTL AND WE OBSERVED THE PRESSURIZATION TO BE NORMAL. WE CLBED BACK TO FL230 AND CONTINUED THE REST OF THE FLT. I BELIEVE THIS WAS A PLT INDUCED PROB RESULTING FROM USING MANUAL CTL INSTEAD OF AUTO. WE BOTH LEARNED THAT IN A 1 PACK OP MORE ATTN MUST BE DEVOTED TO THE OPERATING PACK AND AUTO SHOULD ONLY BE USED.