Unity Animator transition on collision

So I have a chairlift with box colliders moving towards a character with an Animation controller and I have a sit animation state attached to it when it touches the chair. I set the transition from idle to sit and made the condition for it : ShouldSit = true

then I add a script to my character the problem is that when the chair touches the character he doesn't sit!

 var anim : Animator;
 function Start () {
     anim = GetComponent("Animator");
 }
 
 function OnCollisionEnter (col : Collision)
 {
     if(col.gameObject.name == "kedute")
     {
         anim.SetBool("ShouldSit",true);
     }
 }

what have i done wrong? Is there a better way to do this ?