Tyler Watts, putting a 12 v motor in solves the voltage issuse and is more than able to supply the air flow, however,the design of the heater itself is the problem. I ll try to be brief. If you take the heater apart you will find that there is a fan blade that pulls cab air and pushes it thru the heater core. Then the air goes into the box and is directed to the floor or defrost by flicking the flap to desired postion. The biggest problem is the none of this is sealed good enough and there is to much air leakage inside to effectivly get air up the the windshield. Plus by only using in cab air, you are reciculating air and that causes steaming windows and even frost on the inside if windshield esp in colder temps. ( i speak from experince!) Look at any newer heater boxes and you will find better internal sealing, flappers will have foam or soft rubber edges to help with sealing. The heater core is more self contained and the blower will be a cage,not a fan. The whole design is to take outside air directly thru core then directed to wherever you want it. The deluxe heater that is made for the AD trucks is made to pull outside air in. While it is a little more efficient, it still has internal air flow/ leakage issuses. I have had both units apart, and while i havent done any modifications, it is possble to sealup the inside better. It will take some time and a little fabrication and imagination, or go after a retro assy that has todays technology for yesterdays trucks. Which will be just fine, but if you're wanting to stay original you'll have to reengineer the heater to make it more efficient!
