Resetting text variables

Hi, I am wondering if anyone would have an idea as to how to reset a text variable to a blank state via a trigger.  I have built a hangman-type game and created a variable for each letter set to blank as default.  I have the letters fill in the word when selected ie. %Avar%, %Bvar%, etc.  It works fine until I get to the next word (I'm building a multiple word game).  The variables are still set for those letters previously used.  I tried having a trigger set for each letter used on the word to reset the variables:   Avar = (blank), etc,  on the feedback layer but that isn't working.

Thanks, Chris