Sliding Door question

I am trying to make a nice sliding door that opens on trigger enter and stops right below the surface, and closes on trigger exit and stops back at its original position. I decided to try using rigidbody.AddForce instead of using animation because I was running into an annoying mechanic.. Anyways, here's what I got:

 var door : GameObject;
 var speed : float = 20000.0;
 
 function OnTriggerEnter()
 {
     door.rigidbody.AddForce(Vector3.down * Time.deltaTime * speed);
 }
 
 function OnTriggerExit()
 {
     door.rigidbody.AddForce(Vector3.up * Time.deltaTime * speed);
 }
 
 function Update()
 {
     if(door.transform.position.y <= -2.5)
     {
         door.rigidbody.velocity = Vector3.zero;
         door.transform.position = Vector3(0, -2.55, 0);
     }
 }

The door opens smoothly and stops exactly where it should on enter, but when I exit, the door keeps going up.. past where I need it to be. This is my first script and I feel like i'm missing one tiny puzzle piece >.< lol