Defogger now shuts off randomly when lights on heating /ac panel go out and defaults to panel air instead of defogger.

I live in an area where we hit about 110 during the summer which starts in around March or April and ends in November. The AC was working great that was one of my least problems then just all of a sudden it started blowing hot air in the middle of the summer and the lights on the dash flicker on and off. When they are on the AC works ok but once they go off its freaking hot. And IF we get cold during the winter if the lights shut off the heater doesn't blow either.