What was found
MKE/BNA - FLT 1267 - DURING TAXI OUT TO TAKEOFF, FLIGHT CREW FOUND THEY COULD ONLY GET HOT AIR OUT OF THE ENVIRONMENTAL SYSTEM. THE CREW RETURNED TO THE GATE, DEPLANED THE PASSENGERS, AND NOTIFIED MAINTENANCE. MAINTENANCE DECIDED TO PLACE THE ACM ON MEL. THE ACM WAS LATER TROUBLESHOT, FOUND SEIZED AND WAS REMOVED AND REPLACED. AIRCRAFT RETURNED TO SERVICE. (X)