This article is from the Chrysler-Plymouth-Dodge FAQ, by Dr. David Zatz with numerous contributions by others.
You can replace the idler pulley and belt to stop the squeal on the
minivans and some other vehicles. It may go away given a month. On some
vehicles you may need to adjust belt tension, but do not overtighten, or
you will need many expensive new parts!
NOTE Adjusting Caravan belts: A tensioner is below the alternator. Put a
15mm wrench on it and pull down (like you were tightening that bolt) and
the tensioner will rotate and take the tension off of the belt. Much
easier from underneath by removing the splash sheild. That is held by 4
10mm screws. BUT BE CAREFUL!!! I own 2 CC products; an '88 Caravan 2.5L and
an '89 Sundance 2.5L. AC clutch went on both at about 80,000 mi, again on
both about 30,000 mi later, again, etc., etc. Found out that if the belts
are not tightened within specs., it wipes out the bearings SOON!!! Only use
a Burroughs belt tension gauge - about $50.00. NO MORE PROBLEMS!! Hope
this helps. By the way, the Sundance has over 200,000 mi, and the Caravan
has 135,000 - no other serious problems, other than CV boot replacements.