What was found
PIT - FL 1211 - AFTER TAKEOFF, FLIGHT EXPERIENCED PRESSURIZATION PROBLEM AT 12,000 FEET. CREW DESCENDED TO 10,000 FEET. RIGHT PACK WAS INOP AND ON MEL AND LEFT PACK WOULD NOT PRESSURIZE A/C. FLIGHT RETURNED TO FIELD IN PIT AND LANDED WITH NO FURTHER INCIDENT. NO EMERGENCY WAS DELCARED. MAINTENANCE TROUBLESHOT RIGHT PACK AND FOUND AN OPEN WIRE BETWEEN THE P-5 OVERHEAD PANEL AND THE RIGHT AIR CONDITIONING ACCESSORY UNIT. REPAIRED WIRING. THE LEFT PACK WAS TROUBLESHOT TO A FAILED LEFT AIR CONDITIONING ACCESSORY UNIT. REPLACED SAME. OPS CHECK GOOD. (M)