2000 Ford Expedition front A/C blower wont work on any speed?

QUESTION:---

I have a 2000 ford expedition . My A/C blower does not work at any speed, #1 #2 #3 #4, unless I drive down the road at about 55mph or faster and roll the windows down. The air being pulled though the vents seems to "jump start" the blower motor. Once working, the blower will then work at any speed,#1 #2 #3 #4, whether the truck is moving or not. I found lots of threads on here about the switch only working on high because of a bad resistor/limiter, but my problem seems to be different. Any suggestions?
Also, the fan does not work on defrost, heater, or vent mode either, but once I get it "jump started" it works in all modes. I tend to think it is the blower motor itself as opposed to the switch. Any help appreciated.

ANSWER:---

Probably worn out brushes in the motor.bUT ALSO POSSIBLE THE RESISTOR/limiter IS GOT COMPLETELY SHORT.

Confirm by checking for motor drive power when in #4 but the motor isn't turning.

Thanks for the help everyone I left my truck with my mechanic yesterday, and when I went to pick it up, he said "well I couldn't get it not to work" He said he took out the fan and looked at it and was going to change it for me anyway because he figured that was the problem and that it was probably the brushes sticking on the fan motor. When he got it out, no one had a new motor and he could only get it by the next day. Go figure.
Anyway, he gave me a good idea for anyone else who may have this problem. He said if it quits working again, reach under the dash and give the motor a good rap and if it starts working, it's most definatly the motor out. I guess it's the same principle as rapping on a bad starter. But I thought it was a good idea. I think now, if the fan goes out again, I will just change it myself.

------------------

To Order car parts online:--To get heavy discount on car parts .Click this link below:----

http://technoanswers.blogspot.com/2011/05/from-where-to-order-car-parts-online.html

For car error code diagnosis click the link below:---

http://www.automd.com/diagnose/?amdcid=apwldrbrd1

Car no start:--

http://technoanswers.blogspot.com/2011/05/car-will-turn-over-but-will-not-start.html