How to change the fan belts

First go to Nissan's help forum page. Use this link: http://x.nissanhelp.com/forums/index.php

You can get a free login and download up to two files a day using the free login. You want the MA maintenance file of your vans manual. This will include the belt tensions and placement.
You will need to remove the plastic cover on the passenger side of the engine to be able to access the belt tensioners on the alt. and power steering pump. Nissan likes to use the same basic tensioners on most of their stuff. The air pump and air conditioner use idler pulleys, you loosen the bolt in the middle of the pulley enough to allow the pulley to move, no more. there is a bolt with its length toward the center of this pulley, when you loosen this bolt the pulley will start to move down and loosen the belt. repeat this process for both the air pump and the air conditioner. The alt. and power steering you loosen the bolt that secures the tensioner, than you can back off the long bolt in the tensioner to loosen and remove the belts.

I usually check each new built with the old one for length and label its sleeve by function as I take each one off. Makes matching them up when you put them back on much easier.