You are correct..........only the a/c system runs the auxiliary fan on that vehicle.

How did you determine that the auxiliary fan blows the fuse? The fan only runs when the a/c system is on and the system temperature exceeds a specified point. This only occurs when the vehicle is operated at low speeds. The auxiliary fan is generally not engaged for sufficient time to blow the fuse unless the fan is drawing significantly more current than specified. I have my doubts about this.