Vertical camera scrolling fix?

Hello again,

previously I asked a question about how to achieve vertical infinite background scroll; well I was able to come up with the codes below to make the camera scroll down by adding the script to camera but it only scrolls down. I need a fix on this code on how to make it move up. I know its alittle glitch but cant seem to spot it.

Can anyone help?

CODES:

 public float speed = 1.1f;
 public float acceleration = 0.2f;
 public float maxSpeed = 2.5f;




 // Use this for initialization
 void Start () {
 
 }
 
 // Update is called once per frame
 void Update () {

     MoveCamera ();
 }

 void MoveCamera(){
     
     Vector3 temp = transform.position;
     
     float oldY = temp.y;
     
     float newY = temp.y - (speed * Time.deltaTime);
     
     temp.y = Mathf.Clamp  (temp.y, oldY, newY);
     
     transform.position = temp;

     speed += acceleration * Time.deltaTime;

     if (speed > maxSpeed)
                     speed = maxSpeed;

 }

}