As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NUMEROUS INSTANCES OF PRESSURE AIR TEMPERATURE CONTROLS BINDING OR FAILING WHEN COCKPIT KNOB TURNED TO VARY AIR TEMPERATURE FOR COMFORT. HEAT EXCHANGER SHUTTERS BIND UP AND STAYS IN ONE POSITION. SUBMITTER SUGGESTS PART NEEDS REDESIGN; MAINTENANCE PROCEDURES COULD SPECIFY MORE EFFECTIVE LUBRICATION.