As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) CREW HAD ISSUES WITH TRIM AIR VALVE. AFTER RESET ATTEMPTS (AS PER MOC), NO IMPROVEMENT IN CABIN/FLIGHT DECK TEMPERATURE HAD OCCURRED. FLIGHT ELECTED TO RETURN. FLT DECK ZONE TRIM AIR VALVE REPLACED IAW AMM 21-61-02-401 OPS CHECK OK.