Zoom not working, HELP!!

My zoom code is working, but when i start the game it zooms, so i have to hit the z button to unzoom it.This is my script.
#pragma strict

var fov = 90;
function Update()
{
  if (Input.GetKeyDown("z"))
    fov = 10;
  if (Input.GetKeyUp("z"))
    fov = 90;
  if (Camera.main.fieldOfView < fov)
    Camera.main.fieldOfView++;
  if (Camera.main.fieldOfView > fov)
    Camera.main.fieldOfView--;
}

If I am not mistaken, your line 8 will cause line 9 to execute, assuming your camera has a FOV of less than 90. (I think the out-of-the-box value is 60.)