Bykerboy

I have a 2006 Knight with the ISC 330.  The owners manual says two belts, this is not correct.    There is a single belt that drives all of the components including the A/C.  All adjustments are done with tensioner.   I used Napa part number NAPA 25-080830.   I would do what @cbr046 suggested and measure the length you need with a piece of string.   I would also suggest buying a slightly longer and slightly shorter belt and use the one the fits best when bypassing the A/C.   If the belt is too short you will never get it over the tensioner.  You can always return the unused belts (at least here in the US).

Just had the exact same issue on my 2006 Knight.  Added a few ounces of ATF and problem solved!   Thanks for the suggestion.

I purchased replacements from Amazon as well and they fit perfectly.

Replaced mine on my 2006 Monaco Knight.  It is an OEM Chevrolet part:

https://www.amazon.com/gp/product/B000C9SAJC/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1