1996 Subaru Legacy belt slipping

My 1996 outback as finally quit working. The belt has been slipping for a years I replaced it. Now with a fresh tension on the belt it still slips under load and if I cut the compressor off and have the hood up I see the compressor turning backwards, like their is pressure built up downstream? Any ideas appreciated, thanks E.M.

What I’d do in that situation, presuming you’ve already tried a new belt, is remove the belt and make sure all the pulleys/tensioners/idlers in the belt path are silent & turn freely, under hand rotation. No noises, glitches, rough spots over 360 degrees. Double check the belt is on the correct path and square on the pulleys, the pulley surfaces aren’t worn out or damaged, etc, of course; sometimes getting the correct path can be pretty confusing. Another thing to try is spraying a little water from a spray bottle on the belt. Does that change anything about the symptoms?