HVAC Blower Speed Mod Question
 

I really like my 09 FX-4, but there are a few things I would change if I were designing it. One thing is the HVAC Blower Speed Settings.

My truck has the manually controled blower with 4 speed settings. Speed 1 moves almost no air and speed 2 moves just a bit too much. Speed 2 is also just a bit too noisey. It needs a speed between 1 and 2.

Back in the day, the blower resistor units used exposed wound resistors that one could modify by adding or removing coils to change the preset speed of the blower motor, but the new stuff, like my 09, uses a fully encased resistor unit that defys modification.

You can see a photo of it here:

How could one go about modifying one of these units to give different resistance values for the speeds, other than the ones designed into it? If one were to solder in another resistor across the terminals for speeds 2 and 3, that should cause speed 2 to be a bit slower. What value, size and wattage resistor would be needed there?

Id think it would be easier to just put a pig tail in the harness and use a different resistor block all together?

Basically you need to find out what the resistance is on each individual leg of the resistor pack. and to slow down a certain setting you add more resistance, to speed it up you reduce.

For instance if you have 4 speed resistor pack you may see 9 ohms on position 1, 6 ohms on 2 and 3 ohms on 3 and zero on 4. to lower the fan speed on position 2 you would add more resistance to that leg, but make sure you keep it in series. If you add in across the terminals of two legs you are creating a parallel circuit and actually reducing resistance thereby increasing voltage and fan speed.

Basically you need to find out what ohm values your dealing with to determine how much resistance you need to add, but keep it less than the value of position 1 to get what you need. Also you need to use large high wattage resistors, those little 1/4 watt jobs from radio hack will burn up in a heartbeat, you need at least 2 watt capacity.

Thanks 05RedFX4, I was thinking about it incorrectly.

Adding a resistor across 1st and 2nd speed would then increase voltage in speed 1 thus raising the speed of the motor in the first speed. That might be a better solution since 1st speed is nearly useless anyhow.

I'll have to pull the resistor pack and see what the values are and go from there.