As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LEFT AND RIGHT PACKS FAILED ON THE GROUND WITH APU BLEED PACKS ON LOW. FOLLOWED QRH PROCEDURE. TURNED PACKS OFF, THEN ON. BOTH PACKS FAILED WITHIN 15 SECONDS AND SMOKE ENTERED THE CABIN. UPDATE 6/3: BOTH PACKS FAILED ON THE GROUND. REMOVED AND REPLACED LEFT AND RIGHT PACK OVERTEMP SWITCHES. OPS CHECK GOOD. 6/3: REMOVED AND REPLACED GROUND PROXIMITY SENSOR AND HARNESS. OPS CHECK GOOD.