As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED A BURNING SMELL IN THE COCKPIT AND RETURNED TO THE GATE. FOUND THE SMELL COMING FROM THE RIGHT HAND AIR-CONDITIONING PACK. THE LEFT HAND AIR CONDITIONING PACK WAS CURRENTLY ON DEFERRAL. MAINTENANCE DEFERRED THE RIGHT HAND AIR CONDITIONING PACK. NOW THE AIRCRAFT HAS BOTH AIR CONDITIONING PACKS ON DEFERRAL.