mathf.clamp and temp variables stuck!!!!

hi unity peeps ,

I have been trying to figure out for a while now how to apply .clamp to a rotation in c# and was really struggling . I got as far as finding out about needing to store a temp vector3 then using that , but have tried every way I can think of and using lots of docs and tutorials trying to peace things together to try and understand , it was hitting me back with errors and that's okay , gives me something to work with.
but now nothing. I've got this code applied it and no errors but nothing happens ? now its got me confused what it is supposed to do is rotate an object on the y axis and then clamp it so far if someone can have a look and see if they can point out what I am missing would be great , even a point in the right direction would help

Here is my code . and thanks again too such an amazing commUNITY...

using UnityEngine;
using System.Collections;


public class turn : MonoBehaviour
{
public GameObject head;
private float right = 1.0f, left = -1.0f ;
private Vector3 rot;
public Transform headrot ;
// Use this for initialization
void Start ()
{
rot = headrot.eulerAngles ;
left = rot.y;
right = rot.y;


}


// Update is called once per frame
void Update ()
{
if (Input.GetKey(KeyCode.A))
{
left = left * Time.smoothDeltaTime;


print ("rotate left active");


left = Mathf.Clamp(left,-180,180);


headrot.eulerAngles = new Vector3 (0.0f,left,0.0f);
}

if (Input.GetKey(KeyCode.D))
{
right = right * Time.smoothDeltaTime;

print ("rotate right active");

right = Mathf.Clamp(right,-180,180);

headrot.eulerAngles = new Vector3 (0.0f,right,0.0f);

}

}




}