B737 Next Generation Undifferentiated
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Flight Crew Last 90 Days 157; Flight Crew Type 4961
Communication Breakdown
Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
Climbing through approximately 15;000 ft. we had a left pack trip. We leveled off at FL190 and accomplished the PACK non-normal checklist. The left pack light extinguished; but re-illuminated after about a minute. We re-ran the PACK checklist again and the left pack light extinguished again. I suggested to the FO (First Officer) to check the three supply duct temperatures after the second left pack trip. We observed the aft supply duct temperature to be excessively high; approximately 70 degrees C; and rising. I then suggested that we turn the Aft Cab Temp Selector to off. After we did that the aft supply duct temperature seemed to stabilize; but was still high. I noticed the left ram door full open light was illuminated as well. There was also a slight burning smell in the cockpit. I attempted to have the Dispatcher call me in the hopes of getting a phone patch with [Maintenance] via the Call Me prompt. We never heard the Dispatcher over the frequency; and only briefly heard San Francisco Arinc. Arinc attempted several SELACAL's ; but we could hear no one on the designated frequency. I suggested a new frequency to Dispatch via acars; but never heard back. At this point the left pack was stabilized; and we had burned some fuel by staying low. Both the FO and myself felt that it was much safer to return to [departure airport] rather than climb to FL390 with an overheating; compromised pack. We diverted safely and contacted both [Operations Manager] and Dispatcher. We also thoroughly briefed the mechanics at the return gate.
B737NG Captain reported returning to departure airport after twice experiencing left pack trip.