I found that on my Duratec, the fans run on low for a/c or engine warm enough, and high is only in high a/c pressure or very hot conditions that I haven't seen yet here in NY. Basically, low is normal operation. It is possible the fan is too locked up to turn at low speed, it happened on my Dad's Mercury Sable. We could not believe how stiff the fan motor was, had to replace it. You probably could get your fan operating like you did experimentally, but only a short time, till you can fix it right. The fan motor or wiring could burn out.
