question about a/c blower

I have converted my 69 cuda factory a/c to r-134a refrigerant ,replacing all underhood components ( classic auto air kit ) about two years ago. I was never really satisfied with the amount of cooling on hot days 85 +. The temp out of the ducts is around 38 to 42 degrees should be good enough, but never much air flow from vents compared to newer vehicles. Checking last night i only have about 7.5 volts to blower motor in high speed is this normal ? Should it be battery voltage ? I used a jumper wire to feed blower battery voltage what a difference !