DASH 8 FO REPORTS CABIN ALTITUDE WARNING AT 10000 FEET ON CLIMB OUT. PACKS ARE DISCOVERED OFF DURING THE RETURN TO LAND.

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DURING GND OPS; PACKS WERE CYCLED OFF TO ATTEMPT TO WORK THE HEATING-AIR CONDITIONING SYS. THEY WERE NEVER DISCOVERED AS OFF PRIOR TO FLT. THERE IS NOT PROCS FOR VERIFYING THIS; NOR IS IT A CHKLIST ITEM AT ANY TIME. FLT DEPARTED AND EXECUTED TURN FOR DEP. CLRED DIRECT THROUGH ABOUT 8500 FT; AND PROCEEDED ON COURSE. BECAUSE OF QUICK CLB; AND HIGH DEP ALT; THE 'AFTER TKOF CHKLIST' WAS COMPLETED AS WE PASSED THROUGH 10000 FT. JUST AFTER; THE CABIN PRESSURE WARNING ILLUMINATED; AND WE IMMEDIATELY LEVELED OFF; AND FOLLOWED THE EMER ITEMS CHKLIST. WE NOTIFIED ATC AND WERE IMMEDIATELY GIVEN DSCNT; AND TURN TOWARD ZZZ. CAPT QUICKLY INFORMED THE FLT ATTENDANTS THAT IT WOULD BE A RETURN TO FIELD; NORMAL LNDG; 5 MINS. REACHING ABOUT 18 DME WE WERE CLRED VISUAL APCH. DURING THIS TIME; I FLEW THE PLANE; AS CAPT FINISHED THE CHKLIST; AND RECALCULATED FOR OVERWT LNDG. IT WAS AT THIS TIME (AFTER ALREADY ON DOWNWIND) THAT HE REACHED THE ITEM REGARDING PACKS. I BELIEVE HE CYCLED THEM ON AT THAT POINT; AND SHORTLY AFTER THE ACFT BEGAN TO PRESSURIZE. COMPLETING THE NORMAL DSCNT AND LNDG CHKLISTS; WE LANDED WITHOUT INCIDENT; AT LESS THAN 200 FPM DSCNT; AND TAXIED TO THE GATE. I CONTACTED DISPATCH TO ANSWER THEIR QUESTIONS; AND CAPT CONTACTED MAINT. IT WAS DETERMINED THAT THE ACFT WAS SAFE; AND WE THEN CONTINUED ON. 1 PAX RPTED FEELING A LITTLE NAUSEOUS; BUT NOT SURE THAT IT WAS RELATED. I BELIEVE SHE WAS THE ONE WHO DEPARTED THE PLANE; FOR FEAR SHE WOULD NOT BE ABLE TO MAKE HER CONNECTION AND NOT BECAUSE OF ILLNESS. NO OTHER PAX RPTED ANY PROBS; MEDICAL OR OTHERWISE; AND SEEMED REALLY ONLY CONCERNED WITH THE DELAY TO CATCH A CONNECTION. FLT DEPARTED WITHOUT FURTHER INCIDENT. PACKS SELECTED 'AUTO/MAN' IS NOT LISTED ON ANY PROC OR CHKLIST TO RECHK PRIOR TO TKOF. THE ONLY TIME IT IS DISCUSSED IS IN THE CAPT'S ORIGINATING CHKLIST; AND THIS WAS OUR SECOND LEG WITH THAT ACFT THAT DAY; SO THIS CHK WAS NOT ACCOMPLISHED. DURING MY SHORT TIME HERE; I HAVE HAD MORE THAN 10 DIFFERENT EXPLANATIONS AS TO THE WORKINGS OF THE AIR CONDITIONING SYS FROM DIFFERENT CHK AIRMEN; CAPTS; AND FO'S. THERE IS NO CLR GUIDANCE AS THE OP OF THIS SYS FROM THE COMPANY; WE JUST HAVE TO FIGURE IT OUT. FURTHER; I SUGGEST A LINE BE ADDED TO THE 'TAXI CHKLIST' RIGHT BEFORE 'BLEEDS ON': 'PACK -- AUTO/MAN' TO ALLOW SUCCESSFUL OP OF THE AIR CONDITIONING; AS WELL AS PRESSURIZATION OF THE ACFT. I BELIEVE THIS WOULD HAVE PREVENTED THIS RETURN TO FIELD; AND THE FURTHER DELAYS -- DISRUPTIONS TO PAX; ACFT; AND CREWS.