The aux fan for the a/c will not come on if the freon level is low. This is a 2 speed fan , [ low speed for a/c],and it is activated by the high pressure sw. at the reciever/drier. If the freon level is low , this sw. cut in spec. will not be reached due to too low a high side pressure.
I would check both the sight glass for freon level and test the aux. fan circuit by jumping the two wires coming off the high pressure switch. If the fan works with jumper, than suspect freon level low. [ or remote possible bad sw.]
The high speed aux. fan circuit on your model is an aid for engine coolant temp. and is activated by a coolant temp sensor at higher than normal engine temp, regardless of a/c funtion. [ on or off].