As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IN CRUISE AT FL 380 LOUD SURGING OF SINGLE AIR CONDITIONING PACK. LEFT DUCT PRESSURE OBSERVED SURGING REPEATEDLY FROM 25 PSI TO 41 PSI RT DUCT PRESSURE AT 24 PSI(<P>PERFORMED BITE 21-51 FT 803 FOUND LOW LIMIT VALVE HARD FAULT REMOVED AND REPLACED LOW LIMIT VALVE IAW AMM 21-51-11 OPS TEST GOOD LEAK CHECK GOOD </P>)