As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ABQ - FL 184 - FLIGHT RETURNED TO FIELD TWICE AT ABQ DUE TO THE AIRCRAFT NOT BEING ABLE TO PRESSURIZE. NO EMERGENCY WAS DECLARED AND THE FLIGHTS LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE FOUND THE RIGHT MOISTURE SEPARATOR FROZEN. CLEANED SEPARATOR AND REPLACED THE RIGHT 35 DEGREE TEMP SENSOR, SHUTOFF VALVE AND TEMP CONTROL BOX. PRESSURIZED AIRCRAFT. PRESSURIZATION NORMAL. REFERENCE USAASB97009.