As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PDX - FLIGHT 2518 - LEFT AIR CONDITIONING PACK CYCLES OFF AND ON SEVERAL TIMES IN FLIGHT. LEFT PACK SELECTED OFF PER THE CHECKLIST PROCEDURE. LEFT PACK READINGS OBSERVED TO BE ERRATIC AND VARIABLE WITH PACK ON OR OFF. MAINTENANCE PLACED ON MEL 21-51-1A. 3/11. MAINTENANCE REPLACED THE LEFT PACK INLET TEMP SENSOR. OPERATIONAL CHECKS GOOD. AIRCRAFT RETURNED TO SERVICE.