Here's something else (FWIW):
This company: http://www.goexpediter.com/sprinter-expediter-van-price.htm
sells a rear aux A/C unit for the Sprinter van and says:
"Hanvey "Monster Cool" rear cargo area interior air conditioner. 42,000 BTU motive powered air conditioner for temperature sensitive carriers. (Sprinter will idle approximately 3-4 hours on a single gallon of fuel to power the "Monster Cool" while generators with roof top air with only 13,500 BTU will only give you hour hour or less on a gallon to power much smaller BTU rooftop A/C units)."
Wow! If true, that's a huge difference in fuel consumption -- 42,000 BTU for 3-4 hours vs. 13,500 BTU for one hour or less, for one gallon of diesel. I mentioned these aux A/C units in another post but I didn't realize the difference in efficiency was so dramatic.
Of course,this doesn't answer the question of whether it's advisable to idle the Sprinter for extended periods -- Hanvey doesn't have to warranty the engine or pay for repairs -- but I wonder how many of these A/C units they'd sell if M-B recommended not idling for more than 2-3 minutes. They'd be all but useless.
I'm wondering if the warnings about idling from various sources are referring to the stock idle speed, as opposed to the 'high speed idle' factory option.