In My Previous video i have explained in Detail the Wiring , Connections and working of AC Blower and Related components,
   • Car AC Blower Resistor Wirings Workin...  
Here I will explain How to Replace the Traditional Resistive Fan Speed Controller with More Efficient PWM Based Speed Controller.
Why we are doing this, for this you need to view my previous video in this Context but in short
It generates No Heat, More Efficient and Consume less Power.
The Best place to install this speed controller could be just before Fan Blower as I am doing in this video and you can see.
Unplug the Blower Wire 1st.
You need this type of Male/Female wire connector.
PWM Speed controller has 4 connections , Two for Input and Two Output and one the 3rd one is the regulator Knob, that you can place anywhere near the dashboard.
After Joining the wires as shown, connect this speed controller to the Blower Motor as I will be doing here.
Now to Run this module 1st Move the existing Fan Speed control Knob to 4th Position.
And after that you can use the Regulator Knob of PWM speed controller to increase or decrease the fan speed as you can,
But In current scenario , Both Resistive and PWM Controllers are controlling the Blower Speed simultaneously that’s Obviously useless,
So we need to Bypass the Blower Resistor as well.
How we will do that Pretty simply keep the Fan Resistor at its place but Remove it’s wire connector and short all the Wires with some Jumpers wires like these or So,
Keep in mind wires should be Thick as heavy current will flow.
After doing this you existing Fan Speed controller knob at any position (except 0)1,2,3 or even 4 , it will make no difference as speed will only be controlled via newly installed PWM controller knob.

And at last the Best place to install this PWM speed controller could be here , by piercing a hole in the dashboard Plastic and placing this New PWM Controller’s Knob, while the existing knob could be at position except 0, Rest is up to you.