What was found
ON TAXI OUT, THERE GRINDING NOISE AND SMOKE BELLOWING OUT OF THE GASPERS. THE CREW TURNED OFF THE LEFT PACK AND RAN THE SMOKE AND FIRE, FUMES CHECKLIST. THE SMOKE CLEARED. CFR CHECK OUT THE AIRCRAFT. NO FIRE DETECTED. TAXI BACK TO GATE. COMPLIED WITH SMOKE/FUMES IN THE CABIN INSP PER AMM 05-51-56-2 AND FIM 21-00-01-3-0. FOUND LT ACM LOCKED UP AND CAUSING THE SMOKE AND SMELL IN THE A/C. NO OTHER DEFECTS NOTED SEE WRI 21-50 5841 FOR LT ACM R&R CORRECTIVE ACTION. COMPLIED WITH SMOKE/FUMES IN THE CABIN INSP PER AMM 05-51-56-2 AND FIM 21-00-01-3-0. FOUND LT ACM LOCKED UP AND CAUSING THE SMOKE AND SMELL IN THE A/C.