As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON GROUND, PARKED AT GATE, APU RUNNING. TURNED ON LT & RT PACKS. SMOKE BEGAN COMING FROM VENTS IN COCKPIT AND LT PACK AUTOFAIL CAUTION MESSAGE WAS PRESENTED. REMOVED AND REPLACED THE LEFT HAND AIR CYCLE MACHINE ASSY. IAW MM 21-51-08 -PERFORMED OPS TEST OF AIR-COND. SYSTEM - OPS & LEAK CHECKED GOOD. AIRCRAFT RETURNED TO SERVICE.