As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING APU OPERATION AT GATE AND BOTH PACKS ON, NOTICED FUMES IN THE CABIN. SUSPECTED CONTAMINATION DUE TO DE-ICE FLUID COMING THROUGH THE AIR CONDITIONING SYSTEM. REPLACED BOTH LT AND RT WATER SEPARATORS COALESCER BAGS PER MM 21-55-51, OPERATIONAL CHECKED OK.