As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER STARTING THE APU AND BRINGING ON BOTH PACKS, GOT SMOKE INTO THE FLIGHT DECK AND THE CABIN. SMOKE WAS COMING FROM THE AIR CONDITIONING SYSTEM. ALSO GOT A SMOKE CAUTION MESSAGE. REMOVED AND REPLACED BOTH RIGHT AND LEFT ACM WATER SEPARATOR SOCKS WITH SERVICEABLE UNITS IAW MM 21-51-13. CHECKS GOOD AT THIS TIME.