I had a truck in the tropics that didn't have a/c. The defroster didn't help with condensation/fogging of the glass. For that you need dehumidified air, like from an a/c system, or the rain-x anti-fog stuff, which I found to work quite nicely.

'51 Chevy 1/2 ton w/'62 261, HEI, offy, fentons, dual carter/webbers, t-5 & 12 bolt posi