IEnumerator while loop for charge weapon error.

The chargeDmg float doesn't accumulate while fire-button is held down. I've tried editing the IEnumerator different ways and the only way I can get it to work is this way, but am I just returning null instead of the time.Deltatime value to chargeDmg? Is it more efficient in C# to separate methods that must happen simultaneously at run-time into events, members, properties, etc.? I've just started coding so I don't think I"m quite there yet...

 using UnityEngine;
 using System.Collections;
 
 
 
 public class CocoAndGlennAttacksIII : MonoBehaviour {
     
     Animator anim;
 
     public bool isAttacking = false;
     
     public Rigidbody fireball1;
     public Rigidbody iceball1;
     public Rigidbody fireball2;
     public Rigidbody iceball2;
     
     public float speed = 10;
     
     
     public bool attackVectorEast = false; 
     public bool attackVectorNorth = false;
     public bool attackVectorWest = false; 
     public bool attackVectorSouth = false;
     
 
     
     //public float triggerDownTime = 0;
     public float chargeDmg = 0;
     public float chargeTime = 2;
     
     public bool isCharging = false;
     
     Rigidbody clone;
     
 
     
     
     // Use this for initialization
     void Start () {
         anim = GetComponent<Animator>();
 
         
         
     }
     
 
     void Update () {
 
         
         float lastInputX = Input.GetAxis ("Horizontal");
         float lastInputZ = Input.GetAxis ("Vertical");
         
         if (lastInputX  > 0){ attackVectorEast = true;
             attackVectorWest = false; attackVectorNorth = false;attackVectorSouth = false;
         }
         else if (lastInputX < 0){ attackVectorWest = true;
             attackVectorEast = false; attackVectorNorth = false;attackVectorSouth = false;
         }
         else if (lastInputZ > 0) {attackVectorNorth = true;
             attackVectorWest = false; attackVectorEast = false;attackVectorSouth = false;
         }
         else if (lastInputZ < 0){ attackVectorSouth = true;
             attackVectorWest = false; attackVectorNorth = false;attackVectorEast = false;
         }
 
 
         
         if (Input.GetButtonDown("Fire1")){
             AttackCharger();
             isAttacking = true;
             anim.SetBool ("isAttacking", true);
             
             if(!isCharging){
                 isCharging = true;
 
 
 
              }
         }
 
         
              if (Input.GetButtonUp("Fire1"))
             {
 
 
                 if (attackVectorEast == true){
                     anim.SetBool ("isAttacking", true);
                     clone = Instantiate (fireball1, new Vector3(transform.position.x + 2.5f, transform.position.y, transform.position.z-0.5f), transform.rotation) as Rigidbody;
                     clone.velocity = transform.TransformDirection(Vector3.right * speed);
                 Physics.IgnoreCollision( clone.collider, transform.root.collider );
                     
                     Destroy (clone.gameObject, 2); 
                     clone = Instantiate (iceball1, new Vector3(transform.position.x+ 3f, transform.position.y, transform.position.z -0.5f), transform.rotation) as Rigidbody;
                     clone.velocity = transform.TransformDirection(Vector3.right * speed);
                 Physics.IgnoreCollision( clone.collider, transform.root.collider );
                     
                     Destroy (clone.gameObject, 2);
                 chargeDmg = 0;
                 }
                 if (attackVectorWest == true){
                     anim.SetBool ("isAttacking", true);
                     clone = Instantiate (fireball1, new Vector3(transform.position.x - 3f, transform.position.y, transform.position.z-0.5f), transform.rotation) as Rigidbody;
                     clone.velocity = transform.TransformDirection(Vector3.left * speed);
                 Physics.IgnoreCollision( clone.collider, transform.root.collider );
                     
                     Destroy (clone.gameObject, 2);
                     clone = Instantiate (iceball1, new Vector3(transform.position.x+ -2.5f, transform.position.y, transform.position.z -0.5f), transform.rotation) as Rigidbody;
                     clone.velocity = transform.TransformDirection(Vector3.left * speed);
                 Physics.IgnoreCollision( clone.collider, transform.root.collider );
                     
                     Destroy (clone.gameObject, 2); 
                 chargeDmg = 0;
                 
                 }
                 if (attackVectorNorth == true){
                     anim.SetBool ("isAttacking", true);
                     clone = Instantiate (fireball2, new Vector3(transform.position.x- 0.7f, transform.position.y, transform.position.z +1f), transform.rotation) as Rigidbody;
                     clone.velocity = transform.TransformDirection(Vector3.up * speed);
                 Physics.IgnoreCollision( clone.collider, transform.root.collider );
                     Destroy (clone.gameObject, 2);
                     clone = Instantiate (iceball2, new Vector3(transform.position.x+ 0.7f, transform.position.y, transform.position.z +1f), transform.rotation) as Rigidbody;
                     clone.velocity = transform.TransformDirection(Vector3.up * speed);
                 Physics.IgnoreCollision( clone.collider, transform.root.collider );
                     
                     Destroy (clone.gameObject, 2);
                 chargeDmg = 0;
                 }
                 if (attackVectorSouth == true){
                     anim.SetBool ("isAttacking", true);
                     clone = Instantiate (fireball2, new Vector3(transform.position.x- 0.7f, transform.position.y, transform.position.z -2.5f), transform.rotation) as Rigidbody;
                     clone.velocity = transform.TransformDirection(Vector3.down * speed);
                 Physics.IgnoreCollision( clone.collider, transform.root.collider );
                     Destroy (clone.gameObject, 2);
                     clone = Instantiate (iceball2,  new Vector3(transform.position.x+ 0.7f, transform.position.y, transform.position.z -2.5f), transform.rotation) as Rigidbody;
                     clone.velocity = transform.TransformDirection(Vector3.down * speed);
                 Physics.IgnoreCollision( clone.collider, transform.root.collider );
                     
                     Destroy (clone.gameObject, 2);
                 chargeDmg = 0;
                 
                 
                 
 
             }
         
             
 
             
             isAttacking = false;
             anim.SetBool ("isAttacking", false);
             
 
             isCharging = false;
             chargeDmg = 0;
 
         
         }
 
     }
 
  IEnumerator AttackCharger(){
         while(Input.GetButton ("Fire1")){
      if (chargeDmg < 10 ) { 
             chargeDmg += chargeTime*Time.deltaTime;
          yield return null;
             }
 
 }
     }
 
 
 }