What was found
AIRCRAFT WAS GROUNDED. CLIMBING THRU 15000 LEFT PACK LIGHT ILLUMINATED. PER QUICK RESPONSE HANDBOOK RESET AND LIGHT EXTINGUISHED LIGHT ILLUMINATED SECONDS LATER. FOLLOWED QRH PROCEDURES AGAIN AND LIGHT REMAINED ILLUMINATED. FLIGHT DECK EXTREMELY HOT. THE FLIGHT DECLARED AN EMERGENCY AND RETURNED TO MIA WITHOUT FURTHER INCIDENT. THE FLIGHT LANDED OVERWEIGHT AND TAXIED TO THE GATE ON ITS OWN POWER. STANDBY PACK TEMPERATURE CONT VALVE LEFT HAND FOUND CONDITIONED AIR CHECK VALVE SENSE LINE LOOSE AND LEAKING. REPLACED TUBE ASSEMBLY FOR LEFT SIDE AIR CONDITIONING PACK PER AMM 21-00-00. SEE ALSO SDR AALA201810319031 FOR VALVE SENSE LINE.