So what I gather from your question is can the fan run on defrost? Of course it can! Let me explain the functions of the three sliders the ac switch and the fan speed switch.
Your car has three sliding knobs; the upper knob is closed when slid to the left and when slid to the right opens your upper defrost vents. The middle slider knob opens the fresh air vents and is closed when slid to the left and open when slid to the right. The bottom slider knob when slid to the left is closed and when slid to the right opens the vents that direct heat to your feet.
Now let me expain the heater fan switch which is all the way to the right and has 1;2;3;4. This is the fan speed switch and operate the speed of your fans.
Now you also have a AC switch that is on the left. This is the switch you push on to turn on your AC.
Your car has two different fans one fan sits under your radio this is the AC fan. The other fan (heater fan)sits in your engine compartment.When you operate your AC the middle slider must be slid to the left so that fresh air does not mix with the AC air; that would defeat the purpose of AC; AC only works if it recirculates the air inside the car not fresh air. You can direct your AC to go through your defrost by sliding the upper defrost slider open to the right, but since you would be cooling the window this makes no sense.
If Your fans do not operate when you select a fan speed either your
blower motor is worn out which is on the fire wall next to your wiper mechanism or you may have a blown fuse; wiring problem or a bad AC switch.

Cheers
John

PS check out my website www.germanautosalvage.com

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