I recently purchased as 2012 XL F-250. The previous owner said the blower motor "sensor" was bad and had disconnected the fan from the system and "hotwired" a toggle switch to the fan so he could run defroster in the the winter.He had purchased the part to repair it, but never got the job done (I found out, that it requires removal of the dash and heater core!), which I can do, but don't want to, if this can be avoided. Here's what I'm wondering. The resistor pack (as I'd call it) basically has a huge heat sink on it which goes into the heater core. Like this;

My suspicion is that it's on there just to cool down the head dissipated from the resistors inside. But, I'm wondering if there's any temperature sensor in it? Is it anything other than a few resistors? If not, I'm thinking about just connecting a 12 VDC fan (like used in a computer/electronic device) and mounting it to the heat sink. When power is applied to the blower motor, the fan would then blow cabin air across the cooling fins. Hence, I could mount this in an easy to get to place and avoid dash removal. I'll leave the old one in the heater core to act as a "plug" to keep the air from leaking out.

Has anyone tried anything like this? Any reason it wouldn't work?

 

That's actually an electronic module with high current driver transistors inside (rather than passive resistors). The fins are indeed there as a heat sink to dissipate the heat generated by the transistors as they do their job.

As long as you can adequately ventilate the heat sink, there's no technical reason that it shouldn't work.

 

You wouldn't happen to know the pinouts on that connector, would you? I know I can map it out with a multimeter. I'm guessing at least one will be 12V and one ground (since it's plastic mounted). With an electronics background, I'd say there probably wasn't sufficient airflow that caused a failure. Since this is depending on airflow from the blower to cool, it gets less cooling at lower speeds. Generally something like this IGBT or FET or whatever it is last basically forever if power is good and they are kept cool. Usually electronics die from power surges or, dirt plugs up airflow and they get hot.

 

Here you go:

 

I would sure like to know how that works out relocating it, I replaced mine in my 2015 F350 and took the whole dash out because you can't get to the wiring to it.

Good Luck