As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING SCHEDULED FLIGHT, THE CREW EXPERIENCED SMOKE AND FUMES ACCOMPANIED BY A HIGH PITCHED SQUEAL. THE FLIGHT DECK AIR CONDITIONING SYS WAS SECURED AND AIR TURNED BACK. POST LANDING INSP DETERMINED THE FLIGHT DECK STATION COOLING TURBINE TO HAVE FAILED. DEFERRED THE FLIGHT STATION AIR CONDITIONING SYS IAW MEL 21-1A, LP 33737.