Too much air to the windshield may not be a good thing under certain weather conditions. We have a lot of humidity around here. Defrosting and defogging are two very dissimilar circumstances.
I have a motor which can be wired for really fast or not so fast. When I first set it up, I had it wired for really fast.
On a humid, rainy day, that fast blowing fan may as well have blown a constant spray of water on the inside of the windshield (even at the low speed setting of the Harrison toggle switch).
I rewired it for the slower speed and had much less trouble with the a wet windshield.
Just like so many other mechanisms on these old trucks, the engineers always seem to do things for very real purposes.
Carl
