rear defogger

I have a 94 Caprice...The rear defogger comes on but it does'nt stay on long enough to do any good. Can somebody help me?

How long does it stay on?

It's factory set to stay on for 5 minutes and then shut off. You can hit the switch again and it'll run for 5 more minutes.

Please keep in mind that it's a defogger, not a de-icer.

It doesnt stay on 5 minutes...its alot less than that. When it goes off it wont come right back on. Maybe 5 minutes goes by I can push the button and it will come on but only for a minute or two.