Sounds like the same problem I had with a 2002 GP, but it would stay on high speed only at first, even when the car was off.  Took out the fuse for high so the other speeds worked and eventually it quit altogether.  Quote to repair was over 600 to change the panel (switches).

Googled the problem, turns out that is quite common, and did it myself with $40 part. It was the resistor that controls the fan speed failed from water leakage under the cowl area. 

On the GP, the part in question is a small green circuit board with a coil resistor mounted on it.  It plugs into the fan harness and it's located near the fan motor.  Mounts with 2 screws and the coil side faces the inside of the duct work to measure air temperature.   Apparently the GP is notorious for leaking around the windshield cowl and this part gets constant moisture so eventually shorts out, - could be similar issue with yours.

This is with the fan out, (the green part is the resistor unit)

Looks similar to this one:

I tried different control units and eliminated that as the problem.

Any idea where I might access the fan motor in a Montana? These vans are hard to get into...

427carl wrote:

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http://www.youtube.com/watch?v=oO2-H9wh6GE

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At the 3:40 mark you can see a green module that is bolted next to the motor, that is what controls the speeds etc,

I would definitely look at that one, probably your culprit.

Gerry P

Nothing determined with certainty. My best guess at this point is that the motor may be shot.

I took all apart, tested with a voltmeter so the juice is definitely getting there therefor the control switch is working. The module seems to be fine although I'm not 100% sure because when I turn the know to speed 5, I hear a "click." However nothing happens at any speed. The fan itself looks visually healthy.