As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED "INTERMITTENT STRONG ELECTRICAL BURNING SMELL IN FLIGHT. THE SMELL WOULD COME AND GO. BECAME STRONG STARTING AT DESCENT FROM CRUISE. R & R NR 1 AIR CYCLE MACHINE WITH OPERATIONAL CHECK GOOD. A/C WAS APPROVED FOR RETURN TO SERVICE.