The Stovebolt Site Forums The Shop Area The Electrical Bay Putting 12-volt Resistor Heat to the Defroster?

Every year at this time I wonder how I can capture the heat from the red hot 12-volt to 6-volt heater fan resistor for my defrosters.

I have converted to 12-volt and, with the original 6-volt fan motor, the required resistor can get red hot.

Has anyone put this resistor in a metal box which is in line with the defroster tubing? I'd get a much faster, almost immediate, defrosting with this.

Take a look at some gm products from the 60's. What you propose is exactly what the factory did. The multi speed fan switch resister was inserted in the metal defroster duct prior to the flexible defroster tubing. BTW, these factory resisters work great with 6 volt heater motors in 12 volt systems.

Mopar was/is still doing this, I had to replace the resistor network on my wife's Grand Caravan last year when she had no heat.

Tim

Just mount the resistor on a rectangular piece of Bakelite, cut a hole in the blower housing, and mount it with the resistor inside with a couple of sheet metal screws. With air blowing over it, the resistor will last longer, also.
Jerry

(This might be more detail than the average Stovebolter needs but I like messing with stuff like this!)

I found a metal electrical conduit box which accepted 1 1/4" nipples that were just the right size for hooking up to the defroster outlet on the heater and the driver's side defroster hose. I removed the rubber gasket from the box and installed the 2 resistors as shown below. The empty terminal has the wire to the fan.

Resistors for Conduit Box.

I used a piece of radiator hose to connect the box to the defrostor outlet on the heater and attached the other nipple to the driver's side defroster hose.

Conduit Box Installed. Gotta clean up that wiring!

The theory was excellent but you can't beat an experiment. I used 2 temperature sensors down the defroster vents and measured the temps while warming up the engine.

Driver's Side/Passenger Side temps.
-23 deg/23 deg before starting
-29/35
-41/51
-65/82
-122/136 when fully warm

You can't beat the closer proximity of the passenger side defroster vent (and it doesn't have that metal box to heat.

So, I'm glad I isolated the resistors so I don't catch my radio speaker on fire but it doesn't defrost the driver's side faster the way I set it up. Fun anyway.