Auxillary Fan not coming on

Finished my motor swap (91/95 HO),and now the auxillary fan won't come on when the A/C is switched on. I checked all the connections and fuses. Tested the fan with a jumper - it's good. Only thing I can think is the A/C system was discharged - Is it smart enough to know there's no freon? I've got a friend who is gonna come over and pull a vac and put a fresh charge on it, will that fix it? Or did a relay or something just happen to fail while it was sitting for the last month or so. ..

It might the clutch on the a/c willnot lock up if it is low on freon. at least on my 96 recharged and it all worked