You have high speed and low speed that are selectable. Other speeds in between are slaved to the auto button (in between high and low) which is slaved to the temp setting wheel. Set it on auto and make some changes in the temp setting. If all is well your fan speed should change.

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Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.