Originally Posted by dremaldent

Take about 500 lbs extra fuel and then increase thrust on the right engine. It only takes about 70% N2 to deliver the maximum PSI to the PACK. The only downside is that you can't do this while you're moving. I've successfully cooled the cabin to 24 degrees using this technique. Not the most comfortable but at least a safe temperature, and better than canceling the flight by a long shot.

No APU really isn't that big of a deal. Obviously a little more work, but it is still possible to run flights safely unless the temperature outside is over 100 F.