This problem actually started last year but I'm just now trying to address it. My dash fan works intermittently. It doesn't matter what speed I set the fan to, heat or AC. The fan will run for a couple of minutes, shut off and then restart after another 5 minutes or so. This cycle continues on and off. Switching fan speeds has no effect and neither does turning the system off and then back on.
It almost acts like it is on a timer but of course it isn't. I was thinking loose wire somewhere but the cycling seems to be too precise.
I'm no tech, but I would start tracing every wiring connection and splice from the fan all the way to the switch. Then I would replace the switch. If that didn't fix it, then I would call in the pros. Good luck!
Bad decisions make great stories!