You need a new fan speedswitch. I am guessing it mostly does it on high speed. Newt time it stops, touch the switch. If it comes back on, there you go...

Bad news is that the switch isn't sold by itself. Look for the assembly on e-bay. You can also take the switch out of the rear air control and put it in the front.

The only other possibility is a loose connection to theresistor pack-highly doubtful.

 

http://www.roverlandparts.com/index....amp;ProdID=640