Well, after several weeks absent from working on my heater motor problem, the solution finally arrived in the mail. I had done some research into alternative ways of speed controlling DC motors and the following method seemed to be just the ticket, ala moderne.
But before I explain further, the decision was made to replace the original 6 volt blower motor with a 12 volt model from a ’75 Dodge. This was part of a 12 volt conversion upgrade. And I figured that because the truck lost its ‘originity’ some years back there was no need to further antagonize myself with the existing 6 volt motor. A simple Craigslist “wanted” ad produced several quick local hits, one of which was a perfect fit ($25).
Ok, so I had ordered a couple of pulse-width modulated [PWM] motor controllers — one as a spare. These were from an eBay (Chinese) vendor who was selling them at a very reasonable price: under US$6.00 each, including worldwide shipping!
When they arrived I was surprised how well made and just how small the devices really were: roughly 4”x2”x1.5”. A number of colored wires hung out of the crafted aluminum box, as well as a small tethered potentiometer used to adjust the speed.
Testing the device was a piece of cake and everything worked flawlessly: the heater motor spun up from barely moving, through its arc to full speed. This was accomplished by the variable resistor/pot. The unit didn’t even get lukewarm while it was handling the 4.5 amp motor draw. Installing it into the truck proved quite simple — easy to stash. By using a couple of flat washers I was also able to install the potentiometer into the original ½” dash hole formerly occupied by the old heater switch. It was even possible to then friction-fit the original knob over the new pot knob (which acted as a bushing).
Here is a link to a few photos taken of my buckshee test setup complete with heater fan, and new PWM controller:
http://s525.photobucket.com/user/my_pics48/slideshow/Truck%20heaterNote: Methinks if the decision instead was to have kept the original 6 volt motor, then perhaps using a high amperage 12~6 step down buck converter as Denny tested and reported on in an earlier post (and thanks for your kudos, Denny) and then controlling it all with a more appropriate lower-voltage input PWM controller.
My install was not to suggest
the defacto way of controlling motor speed. Others here have addressed this matter quite competently.
But for me it was the most elegant — and cost effective — modern variant
