NUMEROUS MECHANICAL PROBS PROMPTED THE FLC TO RETURN TO DEP ARPT.

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ACFT DEPARTED CVG ABOUT 30 MINS LATE DUE TO ELECTRICAL PROB AT PUSHBACK. APU WOULD NOT ACCEPT PWR. MECH CAME TO ACFT AND PLACED APU ON MCO AS 'INOP.' WHILE PERFORMING AFTER TKOF CHKLIST; I NOTICED L PACK AIR MIX VALVE IN FULL COLD POS. I USED BOTH AUTO AND MANUAL CTL TO ATTEMPT TO MOVE VALVE OUT OF FULL COLD. I CHKED BOTH AUTO AND MANUAL TEMP CTL CIRCUIT BREAKERS AND FOUND THEM TO BE IN NORMAL POS. AT THIS TIME; BOTH PACKS WERE 'ON;' BOTH BLEED VALVES 'OPEN' AND BOTH PACKS WERE OPERATING. AFTER FINISHING THE CHKLIST I TOLD THE CAPT ABOUT THE FULL COLD SETTING ON THE L PACK. IT WAS BECOMING VERY COLD IN THE COCKPIT AND THE CAPT AND I DISCUSSED THE SIT. IT WAS SO COLD IN THE COCKPIT THAT WE CHOSE TO SHUT THE L PACK OFF AND FLY ON TO SYR AT FL250. ABOUT 1 MIN AFTER TURNING OFF THE L PACK; THE R DUCT OVERHEAT LIGHT ILLUMINATED. THIS IS ONLY AN OVERTEMP WARNING IN THE DUCT (IT DOES NOT AUTOMATICALLY SHUT DOWN THE PACK). I IMMEDIATELY TURNED THE L PACK ON AND BEGAN TO DEAL WITH THE R DUCT OVERHEAT. I LOWERED THE DUCT TEMP ON THE R PACK AND PRESSED THE RESET BUTTON TO EXTINGUISH THE DUCT OVERHEAT LIGHT. I HAD TO DO THIS TWICE IN ORDER TO GET THE OVERHEAT LIGHT TO STAY OUT. WE NOW HAD BOTH PACKS OPERATING. WHEN I TURNED TO TELL THE CAPT ABOUT THE PACKS BEING BOTH ON AND THE DUCT TEMP BEING RETURNED TO NORMAL; I SAW THAT HE WAS WORKING WITH THE OVERHEAD ELECTRICAL PANEL. HE TOLD ME THAT WE HAD ANOTHER PROB. THE R CSD OIL TEMP INDICATOR WAS 'PEGGED' ON THE HIGH TEMP SIDE. IF THIS TEMP DID NOT RETURN TO NORMAL; WE WOULD HAVE TO DISCONNECT IT. SINCE IT WAS NIGHT AND THE APU WAS ALREADY 'INOP' WE WOULD HAVE TO BE OPERATING ON ONLY 1 GENERATOR WITH REDUCED ELECTRICAL CAPACITY. SINCE THERE WAS LITTLE MAINT AVAILABLE AT SYR; WE THOUGHT THAT WE SHOULD RETURN TO CVG (ABOUT 70 MI) AND GET THE ACFT REPAIRED BY OUR MAINT AT CVG. WE TRANSFERRED ACFT CTL AT ABOUT 15000 FT AND 75 MI FROM CVG. THE CAPT COORDINATED WITH ATC/FLT CTL/MAINT COORD TO RETURN TO CVG AND GET THE ACFT REPAIRED. I FLEW THE ACFT BACK TO CVG FOR AN ILS TO RWY 18L IN VISUAL CONDITIONS. APCH; LNDG; AND RETURN TO THE GATE WERE NORMAL. THE CSD OIL TEMP RETURNED TO NORMAL LIMITS DURING THE DSCNT. WE TURNED THE ACFT TO MAINT AND TRANSFERRED TO ANOTHER ACFT FOR THE FLT TO SYR. WE DID NOT RETURN DUE TO A PRESSURIZATION PROB. AT NO TIME WERE BOTH PACKS OFF. AT NOT TIME WAS THE ACFT UNPRESSURIZED OR DEPRESSURIZED. WE RETURNED TO CVG BECAUSE OF THE MULTIPLE MALFUNCTIONS IN THE APU/CSD/PACK TEMP VALUE; AND THE AVAILABILITY OF MAINT AT CVG AS OPPOSED TO SYR.