As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE, CREW NOTED A SMELL OF BURNING RUBBER, ACCOMPANIED BY LOW CABIN PRESSURE LIMITED TO 4 PSI AND THE CABIN TEMPERATURE WOULD ONLY WARM UP TO 45 DEGREES F. MAINTENANCE FOUND THE LEFT BLEED INOPERATIVE, AND FOUND BOTH LEFT ENGINE PRECOOLER VALVES STICKING. THE VALVES WERE CLEANED AND LUBRICATED. SYSTEM THEN OPERATED CORRECTLY, CABIN PRESSURIZED NORMALLY AND CABIN TEMP OPERATED CORRECTLY.