B767 FLC HAS 'CABIN ALT WARNING' DURING CLB; DECLARES EMER AND RETURNS TO KLAX.

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DISPATCHED WITH R PACK INOP; BECAUSE OF INABILITY TO CTL. THE CABIN TEMP SEEMED TO BE COOLING ON THE GND WITH THE L PACK ONLY. AFTER TKOF; WE WERE HOPING TO SEE A DROP IN CABIN TEMP; BUT IT DID NOT; AND WE WERE BUSY TROUBLESHOOTING. WE HAD BRIEFED SINGLE PACK OP AND TO BE AWARE OF PRESSURIZATION; AND IT SEEMED TO BE WORKING FINE; SLIGHT CLB AFTER TKOF 300 FPM. NEXT; WE GOT A 'CARGO DET AIR' STATUS MESSAGE AND RAN THE EMER CHKLIST. THAT PROB WAS CORRECTED AND WE RETURNED TO THE TEMP. I HAD LEVELED OFF AND WAS PLANNING TO RETURN TO LAX; BUT THOUGHT WE WOULD GIVE MAINT A CALL FOR A LAST IDEA. MAINT SAID TO REINSTATE THE R PACK. AT ABOUT THAT TIME WE RECEIVED A 'CABIN ALT WARNING.' WE DECLARED AN EMER; AND STARTED TO DSND. WITH BOTH PACKS OPERATING; THE CABIN WAS STABLE AND STARTED TO DSND FROM 9500 FT. WITHIN 3 MINS THE CABIN WARNING WAS GONE AS CABIN WAS NOW BELOW 8000 FT. WE RETURNED TO LAX WITH A SUCCESSFUL OVERWT LNDG 292000 LBS. THE CABIN ALSO STARTED TO COOL DOWN WITH THE R PACK BACK ON. NEITHER THE FO NOR MYSELF FELT ANY DISCOMFORT IN OUR EARS OR OTHER SIGNS OF A PRESSURIZATION PROB. THE HOT DAY AT LAX; AND TEMP CTL PROB; AND CARGO DET AIR MESSAGE TOOK OUR ATTN AWAY FROM THE CABIN ALT; AND I CAN ONLY SPECULATE THAT THERE WAS SOME UNKNOWN PROB CAUSING THE CABIN TO CLB THE WHOLE TIME. CABIN ALT REACHED 9500 FT THAT I SAW; AND THEN BECAUSE THEY FELT DIZZY; THE #3 FLT ATTENDANT WAS UNABLE TO WALK OFF THE ACFT; AND WAS TAKEN TO MEDICAL. WE SWITCHED ACFT AND CONTINUED TO JFK. IN RETROSPECT; THE ACFT SHOULD HAVE BEEN COOLING SOONER.