As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PHX - CREW REPORTED TAIL COMPARTMENT TEMPERATURE HIGH LIGHT ILLUMUNATED. ACCOMPLISHED QRH PROCEDURES. EMERGENCY DECLARED FLIGHT RETURNED PHX LANDED WITHOUT INCIDENT. AIRCRAFT REMOVED FROM SERVICE. REPLACED BOTH TEMPERATURE SWITCHES AND SEALS ON AUXILIARY POWER UNIT COOLING DUCT. SYSTEM, GROUND CHECK NORMAL OPERATION.