As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD - FLT 1666 - EN ROUTE ORD-ALB, TAIL COMPARTMENT HIGH TEMP LIGHT ILLUMINATED DURING CLIMB-OUT AT 24,000 FEET. RETURNED AND LANDED ORD WITHOUT INCIDENT. REPLACED UPPER RETURN SYSTEM AIR CONDITIONING DUCT. SYSTEM GROUND CHECKED NORMAL OPERATION. (M)