Rear Defrost Problems

[red93gagt]

Hi, I have a question about my rear defrost (93 GA GT 3.3L V6). When my back window fogs up, I press the button for the rear defrost. The little light comes on and the window starts to defrost. After about a minute, the light starts blinking, and the back window stops defrosting. Why is this happening? When it starts blinking, I just turn it off and then turn it back on, so that it can finish defrosting. The rear defrost element (in the window) works, so I think it's a problem with the heating controls.(Maybe?)
Thanks!
Kurtis
(red93gagt)