What was found
DURING CLIMB, CREW REPORTED A LAVATORY SMOKE WARNING AND A MILD ODOR WITH NO VISIBLE SMOKE. ACFT RETURNED TO FIELD & LANDED WITHOUT INCIDENT. MX TROUBLESHOT FAULT TO THE NR 2 BLEED SYSTEM. BOTH PRECOOLERS HAD BEEN CHANGED THE NIGHT BEFORE FOR SCHEDULED MX & NR 2 PRECOOLER REPLACED AGAIN. FAULT RETURNED THE NEXT DAY & WAS TROUBLESHOT TO THE NR 2 PACK. MAINTENANCE FOUND THE RIGHT-HAND PACK DUCT OVERTEMP SENSOR SHEARED OFF. THE OVERTEMP SENSOR WAS REPLACED AND THE DEFERRAL CLEARED. THE NR 2 PACK WAS AGAIN WRITTEN UP FOR ODOR AND WAS DEFERRED. THE NR 2 PACK IS CURRENTLY ON MEL AND THE FINAL CORRECTIVE ACTION WILL BE SUBMITTED AS A SUPPLEMENT TO THIS REPORT. WHILE TROUBLESHOOTING THE DEFERRAL ON PACK NR 2, MAINTENANCE FOUND FOD IN THE DUAL HEAT EXCHANGER FOR PACK NR 2 TO BE THE SOURCE OF THE ODOR. THE DUAL HEAT EXCHANGER WAS REPLACED WITH NO FURTHER DEFECTS NOTED.