As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CLIMBING THROUGHT FL210, ALL AIRFLOW FROM GASPERS STOPPED CABIN STARTED TO SLOWLY CLIMB. WE STARTED A EMERGENCY DESCENT AND RETURN TO DEPARTURE. REPEAT WRITE UP. ACFT RETURNED TO DEPARTURE AFTER T/O. R & R HEAT EXCHANGER IAW AMM 21-51-07, ITEM 45B (21-51-00). OPS CHECK GOOD, NO DEFECTS FOUND AT THIS TIME.