if the fan is running at a really low speed, it's made like that to help push any exhaust fumes away from the inside. if it's running at a higher speed, you may have a short in the blower resistor pack.
good looking wagon, and love the story behind it. I've had a couple cars in my past (they may not have been desirable ones) that I would've loved to have had back, so always cool to read about some of you have been able to get yours back and improve upon it. looking forward to watching this one progress, as I hope to get started soon on the "Gypsy wagon".