The blower motor switch, on the AC/Heater Control Panel, can be easily tested without having to remove it.
In this tutorial, I'm gonna' show you how to test it by going thru' the blower resistor assembly's connector (which is easy to access and is located in the engine compartment's firewall).
You don't need any expensive diagnostic tools for the test since we can easily test it with a 12 Volt automotive test light.
Contents of this tutorial at a glance:
You can find this tutorial in Spanish here: Cómo Probar El Interruptor Del Motor Soplador (1991-1996 3.9L V6 Dodge Dakota) (at: autotecnico-online.com).
The following tutorial will help you test the blower resistor assembly: How To Test The Blower Motor Resistor (1991-1996 3.9L Dodge Dakota).
CIRCUIT DIAGRAM: You can find the blower motor circuit diagram here: Blower Motor Circuit Diagram (1991-1995 3.9L Dodge Dakota).
Blower Motor Switch Basics
The blower motor switch (which is located on the AC/Heater Control Panel of your 3.9L V6 Dodge Dakota) is the component that lets you choose the blower motor speed.
The four blower motor speeds are: LO (low), M1 (medium 1), M2 (medium 2), and HI (high).
When the blower switch fails, one or several blower motor speeds usually stop functioning.
In a nutshell, selecting one of the three blower speeds causes current (that's passing through the blower motor resistor) to be channeled thru' one, or two or three resistor coils (in the blower resistor assembly). The end result of this 'channeling' is a reduction in the blower motor speed.
Here's a more detailed explanation:
- When you select LO speed, the current is channeled through three resistor coils in the blower resistor assembly.
- When you select M1 (medium 1) speed, the current is channeled through 2 resistor coils in the blower resistor assembly.
- When you select M2 (medium 2) speed, the current is channeled through one resistor coil in the blower resistor assembly.
- When you select HI speed, the current is channeled through a wire with no resistance in the blower resistor assembly.
CIRCUIT DIAGRAM: To get a better idea of these different circuits, take a look at the blower motor circuit diagram here: Blower Motor Circuit Diagram (1991-1995 3.9L Dodge Dakota).
TEST 1: Testing The LO Blower Speed Circuit
As I mentioned at the beginning of this tutorial, it's not necessary to remove the AC/Heater Control Panel to test the blower motor switch.
What we'll do is a couple of circuit continuity tests with a 12 Volt automotive test light on the blower resistor assembly's electrical connector to find out if the blower switch is bad or not.
These tests are possible because the wires of the blower resistor assembly connector connect directly to the blower motor switch. Allowing us access to the blower motor switch's internal circuits without having to remove it from the AC/Heater Control Panel.
CIRCUIT DIAGRAM: Blower Motor Circuit Diagram (1991-1995 3.9L Dodge Dakota).
These are the test steps:
- 1
Disconnect the blower resistor from its electrical connector.
NOTE: This and all the other tests are done with your 3.9L V6 Dodge Dakota's ignition key in its OFF position. - 2
Select blower motor speed LO on the AC/Heater Control Panel.
- 3
Connect the 12 Volt test light's alligator clip to the positive (+) battery terminal of your Dodge Dakota's battery.
- 4
Probe the female terminal identified with the #5, of the blower resistor assembly's connector (see photo above), with the metallic point of your 12 Volt test light.
Female terminal #5 has a tan (TAN) wire connecting to it. - 5
The 12 Volt test light should come on if the LO circuit is OK.
Let's examine your test result:
CASE 1: The 12 Volt test light turned on. This is the correct test result.
Now that you've made sure that the LO speed circuit (inside the blower switch) is OK, the next step is to test the M1 speed circuit. For this test go to: TEST 2: Testing The M1 Blower Speed Circuit.
CASE 2: The 12 Volt test light DID NOT turn on. This test result lets you know that the blower motor switch is defective.
