1969 Barracuda AC operation

If you have a 3 speed, I think you should have you have 2 resisters on / by the fan motor. Maybe even in the air box.

Low would be one resister or combination of the 2, med would be another resister or combination of the two and high would be no resister
I could be VERY wrong here but I think that's how it works..

Mymopar.com should have a Factory Service Manual that will detail hay to test