am changing the belts (ac & alternator) on my friend's 86 wagon. It looks like the belt that is on the AC is too small, and the parts store just matched the belt numbers, so the new looks to be too small too. Other than the tentioner, is there anything else to loosen this belt?

make sure the parts store is looking up for the right size motor , there should be adjustment left after you put the new belt on

It's not a dealer installed a/c system (outboard compressor), is it? I recently had what sounds like a similar experience with a friends '88 wagon.

 

The original belt broke and is out gracing the side of an Interstate somewhere, so the replacement belt I got was from Napa and correct according to their books (# 9480) for the outboard mounted compressor configuration. The first belt I got wouldn't go on even with the adjuster at its all the way "in" limit. So I went and got one 0.5 inch longer and it went on, but when I tried to adjust it there wasn't enough adjustment to get it tight.

 

So I went back to the first belt that I had tried and managed to "roll" it on and then adjust it. The adjuster wound up very nearly at it's limit. It's been about a month now and I haven't heard of any problems from my friend, but I told her to listen for a squeal ( indicating a slipping belt) whenever she turns on her a/c (which has been a lot lately).