Interesting idea.
A while back a friend did let me scavenge from his old derelict '79 Bronco.
Thinking it might work out, I scooped the 12 volt heater blower motor and resistor array from the heater box.
The (vented) blower motor was rusty inside (hood was left open) and had a big shroud mounted to it as part of the casing (still spins though).
The resistor array is still in one piece albeit also rusty -- but useable. My concerns are a)having to cut into the vintage heater box to properly mount it b)having enough cooling airflow over it from the puny 6 volt motor and 4-blade fan c)mounting an ugly non-OEM 3-speed non-rheostat switch in/under the dash.
There is a simple way to address the problem- - - -use a speed control resistor designed for multi-speed fans on 12V systems that mount inside the air box with air flowing over it to control the heat generated. By connecting the various speed control windings in parallel, you can get the speed you're looking for. Virtually all 12V climate control systems have those reisitors- - - -go junkyard scavenging and find one you can adapt to your application.
Jerry
