AdMob Interstitial ads. How to make them work?

Hey. The update 4.14 finally came the realization interstitial ads
Total has been granted 4 new function Load Interstitial Ad,** Is Interstitial Ad Available**, Is Interstitial Ad Requested and Show Interstitial Ad

First, I call the Load Interstitial Ad and check whether the request was successfully Is Interstitial Ad Requested if there is no repeat in a few seconds.
At the end of the level, I check whether Is Interstitial Ad Available ads loaded and if so show ads Show Interstitial Ad
And all would be well. … But it works only once.
In the AdMob are no restrictions on demonstrations there.
Your ideas?