As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED CABIN COULD NOT WARM UP IN AUTOMATIC MODE, INSPITE OF TEMPERATURE INCREASE ON POTENTIOMETER. UPON EXAMINATION INSIDE OF DUCT PN 721-407 WAS FOUND TO HAVE INSULATION AND INTERIOR MESH COLLASPED RESTRICTING AIR FLOW. CAUSE OF COLLAPSE, UNKNOWN. THERE IS NO INSPECTION REQUIRED FOR THIS DUCT AND MATERIAL CONSTRUCTION SHOULD ALSO BE REVIEWED.