As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 6479 - IAD-EWR - DURING TAXI, RETURNED TO GATE DUE TO LEFT DUCT OVER TEMP WARNING LIGHT ILLUMINATED. MAINTENANCE INSPECTED AND FOUND ACM STUCK. MAINTENANCE FREED STUCK ACM. OPS CHECK OK. AIRCRAFT WAS RELEASED AND APPROVED FOR RETURN TO SERVICE. (M)