The Nissan Path

So I changed the idler pulley on my 2004 Nissan pathfinder and when j tighten the pully it won't turn it's a brand new pulley and iv never had this problem the old pulley need help can't run my A/C OR HEAT need help

Usually there's a spacer with the pulley, so make sure the spacer is installed in the right place and the pulley is installed with the correct side out, if there is a difference.