As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CABIN RATE OF CLIMB INDICATOR CLIMBS AND DESCENDS AT +/- 500 FEET PER MINUTE IN CRUISE WITH AN AUDIBLE CHANGE IN CABIN AIRFLOW. LEFT DUCT PRESSURE FLUCTUATES APPROXIMATELY 5 PSI AT THE SAME TIME THE CABIN RATE OF CLIMB FLUCTUATES. GROUNDED - YES. ACCOMPLISHED B737-900 FIM 21-33 TASK 802 STEPS C,(1)(A)&(B). REMOVED & REPLACED L/H PACK TCV REF B737-900 AMM 21-51-10. BITE TEST SHOWS NO FAULTS & LEAK CHECKED GOOD. PRESSURIZED ACFT TO 3 PSI. ACFT RATE OF CLIMB INDICATION WAS STEADY NO FLUCTUATION.