Since this question, or variations of it, comes up quite often I thought I’d write a thorough how-to which can be linked to or (hopefully) found in a search.
Your heating & air conditioner blower motor suddenly stops working, only works on certain speeds, or just seems to not blow as hard as it used to.
Applies to (as far as I know):
2001 – 2007 Durango
2001 – 2004 Dakota
99.9% of the time your blower motor resistor block has gone bad. The resistor block is part of the ground path of the blower motor circuit, which in conjunction with the fan speed selector switch controls the speed of the fan by varying the amount of resistors in the electrical path (more resistors = slower speed, fewer resistors = higher speed). This is an easy fix and the new part costs less than $20. If you’re like me and would like to know for sure, read ahead to the “Troubleshooting” section. If you want to play the percentages and just go ahead and change it, skip ahead to the “Removal & Replacement” section.
In order to troubleshoot the resistor block it will be easiest if it is removed from the truck (see Removal and Installation in post #2). Use the following diagram for this procedure.
Pin 2 at the top left goes to the motor, 1, 3, 4, & 5 go to the switch. What happens is a positive source is routed through a fuse and the ignition switch straight to the motor. The ground for the motor is routed through the fan speed selector switch and in turn the resistor block. When you rotate your switch, you are actually controlling the routing of the motor ground through this resistor block. Notice how if the ground goes through pin 5 then out pin 2 it has to pass through 3 resistors? That would be your low speed. See how there is a direct path between pins 1 and 2? That is your high speed. More resistors, lower speed.
If you look closely at the plug, you can read the pin numbers. Older styles may not have these numbers, so use the following picture:
With the connector tab at the top, pin 1 is on the left, pin 5 on the right.
It may also be on the vehicle side of the plug:
Measure from the following points (you should see approximately the following readings).
pin 2 to pin 1 = 0.2 ohms (very little resistance)
pin 2 to pin 3 = 0.7 ohms (some resistance)
pin 2 to pin 4 = 1.3 ohms (more resistance)
pin 2 to pin 5 = 2.4 ohms (most resistance)
If any of those combinations have no continuity, something is wrong with the resistor block. If all those resistance readings are correct, or you just love troubleshooting, you can do the following two steps by disconnecting the blower motor plug. (Here is what you’re looking for, follow the black and green wires around towards the front of the truck to find the motor plug)
1. Disconnect the blower motor plug (seen disconnected in the following picture, for this step you want the plug indicated by the blue arrow) and connect a wire between pin 2 and ground, then between pin 1 and a 12v source (fuse block, battery, etc…). This will verify the blower motor functions correctly. Notice in the picture the plug is held up by two friction tabs, you can pull down and release those tabs for easier access.
2. Using the following diagrams, and with the blower motor plug disconnected, connect one lead of your meter to pin 1 of the vehicle side of the plug (Red arrow), then the other meter lead to a suitable ground. Verify the resistor block is plugged in to the vehicle harness. Rotate the fan speed selector switch through all the positions and watch the resistance change on the meter (should be similar readings as above). This will verify your speed selector switch and all the wiring has proper continuity. If any resistance reading seems incorrect, and you have already separately checked the resistor block, continue to troubleshoot the speed selector switch and the electrical connectors themselves.
Continued in post #2