As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ATB/PRESS- RETURNED MCI DUE TO AIRCRAFT WOULD NOT MAINTAIN CABIN PRESSURIZATION. LEFT PACK ON MEL. FOUND RUBBER SLEEVE BETWEEN ACM AND HEAT EXCHANGER SPLIT. REPLACED SAME. PERFORMED SINGLE PACK CONFIDENCE CHECK. OPS CHECK GOOD. (LOG 8323450 - AIRCRAFT WAS GROUNDED)