As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PDX - ON TAXI FOR FLIGHT 2475 RETURNED TO THE GATE WITH NR 1 AIR CONDITIONING PACK NOT ON-LINE. PLACED ON MEL 21-51-1(A). RETURNED TO SERVICE. ON 12/20 MDC INDICATES LEFT FLOW CONTROL VALVE NO RESPONSE TO COMMAND. REMOVED AND REPLACED LEFT FLOW CONTROL VALVE IAW CRJ AMM TASK 21-53-14-000-801-A01 AND 21-53-14-400-801-A01. OPS CHECK GOOD, NO LEAKS NOTED. PERFORMED SEVERAL ENGINE STARTS. NO DEFECTS NOTED. AIRCRAFT RETURNED TO SERVICE.