As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PLANE DID NOT DEPRESSURIZE UPON LANDING. SWITCH IN AUTO OUTFLOW VALVE SHOWED CLOSED. ACFT GROUNDED. SWAP CPC, FAULT MOVED WITH CONTROLLER. MOVED BACK TO ORIGINAL POSITION. REPLACED NR 2 CPC IAW MM 21-31-01. PERFORMED PRESSURIZATION SYS. GROUND TEST FOR BOTH CPC, REF MM 21-31-00, TEST PASSED.