Why is my admob interstitial working fine in xcode simulator but not on my test devices (iphone 4s & ipod 5th gen)?

Question

So I have this app that has both an admob banner ad and an interstitial ad. The banner runs fine on all screens. The interstitial ad is only supposed to load on one screen --

Answer 1

You are attempting to present your interstitial before it has a chance to load. Your timer fires func presentInterstitial after one second. Change this to a larger number to give the interstitial time to load.

import UIKit
import GoogleMobileAds

class ViewController: UIViewController, GADInterstitialDelegate {

    var admobInterstitial : GADInterstitial?
    var timer : NSTimer?

    override func viewDidLoad() {
        super.viewDidLoad()

        admobInterstitial = createAndLoadInterstitial()
        timer = NSTimer.scheduledTimerWithTimeInterval(5.0, target:self, selector: Selector("presentInterstitial"), userInfo: nil, repeats: false)
    }

    func createAndLoadInterstitial()->GADInterstitial {
        var interstitial = GADInterstitial(adUnitID: "yourAdMobADUnitID")
        interstitial.delegate = self
        interstitial.loadRequest(GADRequest())
        return interstitial
    }

    func presentInterstitial() {
        if let isReady = admobInterstitial?.isReady {
            admobInterstitial?.presentFromRootViewController(self)
        }
    }

    func interstitial(ad: GADInterstitial!, didFailToReceiveAdWithError error: GADRequestError!) {
        println("interstitialDidFailToReceiveAdWithError:\(error.localizedDescription)")
        admobInterstitial = createAndLoadInterstitial()
    }

On a side note, you should not give a local variable the same name as a global variable.