As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING DESCENT, CABIN PRESS ERRATIC IN AUTO & STANDBY MODES. FOUND OUTFLOW VALVE HEATER INOP CAUSING OUTFLOW VALVE TO FREEZE. REMOVED AND REPLACED AFT HEATER AND OUTFLOW VALVE PER MM. PERFORMED PACK CONFIDENCE CHECK PER SWA SAM 728 & CABIN PRESS CONTROLLER TEST PER SWA SAM 729. OPS CHECK GOOD.