As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB-OUT FROM KTOL, WHEN LEFT AIR CONDITIONER PACK MADE A LOUD BANG, TURNED ON AND MADE EXCESSIVE NOISE WHILE TURNED ON. THE CREW RETURNED TO KTOL AND LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED THE AIR CONDITIONER PACK AND FOUND LEFT GROUND CONTROL RELAY STUCK VIA LEFT SQUAT SWITCH CLEANED ELECTRICAL CONNECTOR AND RESEATED TO LEFT SWITCH. OPERATIONAL CHECK WAS GOOD IAW DC8 MAINTENANCE MANUAL 21-55-5. AIRCRAFT WAS RETURNED TO SERVICE.