Originally Posted by IAHB756

Exactly. On the 737 on hot days, single engine taxi actual cools the cabin better than running both (if you are running both packs off of the engines). Why? We use #2 (the right) engine for single engine movement. It is normally operating at a slightly higher RPM (read, more pneumatic pressure feeding the pack) and the left pack is getting constant high pressure from the APU. EWR 4R departure last Summer. I’m DH in row 21. Captain taxis out on number 2. Cool cabin and nice smooth taxi. Starts number 1 while still number 8 or something. Cabin begins to warm up by the time we are next for departure as both engines at idle (lower pneumatic output). Wish he had waited a tad longer (for comfort reasons). Max taxis easy on 1 engine. In fact, easiest way to operate from our busy hubs is crank 2 ASAP. Run after start and get taxi clearance. Start moving and clear the alley for others then have the option to start the left immediately upon taxi or, if conditions permit; hold off until you see fit