I finally chose APU bleed air over the ground cart in Billings and it cost me an hour
Had a 737 with a dead APU and I had to pick between a ground air cart or letting the engine bleed do the pack start. Went with the cart at -8F in Billings and the damn thing iced up twice before we got one pack online. Anyone else had a cart quit on them in cold weather and just gone to engine bleed instead?
Pretty sure a 737 can't do a pack start off engine bleed on the ground, only the APU or a cart can push the packs. Engine bleed does the anti-ice and pressurization once you're up, but on the ground the packs need that high pressure air from somewhere else.