Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 40; Flight Crew Total 16700; Flight Crew Type 3777
Distraction; Situational Awareness; Troubleshooting
Aircraft Equipment Problem Less Severe
Flight Crew Returned To Gate; General Maintenance Action; General Flight Cancelled / Delayed
Environment - Non Weather Related; Aircraft
In the blocks the right pack tripped twice. Both times we submitted an ELB [Electronic Log Book] entry and maintenance was able to get it to reset after a fairly long cool down period. They felt it was the excessive heat in ZZZ and that it would operate normally on engine air. During taxi out with both engines running; we noticed an approximately 1% difference in FMC N1 limit values with the right side being higher; but no warning lights illuminated. This coupled with the flight attendants calling to report no airflow and excessive heat in the rear of the aircraft made it clear that there was a much bigger cooling issue. We tried various configurations to cool the rear of the airplane to no avail. As passengers were beginning to get up and express their discomfort we advised ground and ramp that we needed a gate return and that it was too hot to trouble shoot away from the gate. Maintenance later determined the problem to be the air cooling machine. Maintenance wanted to defer the pack inop. Dispatch refused a deferral due to the incredibly hot temperature in ZZZ. I fully agreed with the refusal due to our inability to keep the rear of the aircraft cool on initial taxi and COVID air flow concerns. A spare was found and the flight continued to destination. Flight was fully debriefed.
Air carrier Captain reported an air cooling machine issue during taxi out resulting in excessive heat in the rear of the aircraft and a return to gate. Maintenance reportedly wanted to defer the issue; but the crew and Dispatch decided against it and opted for an aircraft swap.