Mastercool Won't Work On Auto

I have a ten year old Mastercool. I noticed last summer when it's on Auto mode the fan motor will shut on and off, on and off, until I can jump up from what ever I'm working on and push the Auto button to shut it off and push the fan button so the fan stays on high all the time. The unit has the original two speed motor from ten years ago.
Is there someway that I can find out if the problem is in the motor or the control box on the unit it's self.
Thanks, Dave