As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT FL380 UNABLE TO CONTROL UPPER DECK TEMP€™S. THIS WAS APPROX 1.5 HRS INTO FLIGHT AFTER TALKING WITH MX, DISPATCH AND 5ME, DIVERT BACK TO ANC WAS DECIDED. REMOVED AND REPLACED IASC #1. UPDATED AND VERIFIED SOFTWARE AS PER DASH 8 MATRIX REF AMM 36-10-01-470-802 AND 36-10-01-400-801 ALL TEST PASS. NO MESSAGES AND NO EXSITING FAULTS.