Nate,

How long do you leave it on? It takes a few minutes to begin to defog or defrost the glass.

Also, have you cleaned the window with anything sharp that may have broken one of the "wires" They are relatively fragile and if there is a break in continuity, the grid won't heat.

You could use a voltmeter to check if power is flowing to the grid, and then check each grid line until you find a break. If not there, there may be a break in either the power or ground wires to the window.

Bryan