As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER PUSHBACK THE CREW RECEIVED THE SMOKE AFT LAV WARNING AND SMELLED A BURNING ODOR. THE PASSENGERS WERE EVACUATED THROUGH THE PASSENGER DOOR AND THE AIRCRAFT WAS TOWED BACK ONTO THE GATE. MAINTENANCE REMOVED AND REPLACED THE NR 1 AIR CONDITIONING SYSTEM CONTROLLER. THE SYSTEM OPERATIONALLY CHECKED GOOD AND THE AIRCRAFT WAS RELEASED FOR SERVICE.