Stereo & Electronics - defrost switch trouble.

Why would my defrost only stay on for like 30 secs sometime and stay on forever other times!!!??? When i go to work (cold out and fog on the window) it takes two or three trys to keep it on, then once thats over with it will stay on forever.Someone explain? bad switch? or is there a ciruct breaker?

It is usually caused by the circuit breaker in the fuse panel. I had the same problem. Just replace the circuit breaker with the same amperage fuse (30 amp) and the problem should go away.