The blower motor resistor assembly can be tested with just a multimeter and in this tutorial I'll show you how.
With the your test results you'll be able to find out if the blower motor resistor is defective or not.
Contents of this tutorial at a glance:
You can find this tutorial in Spanish here: Cómo Probar El Conjunto De Resistencias Del Soplador (1990-1995 3.0L Nissan Pathfinder y Pick Up) (at: autotecnico-online.com).
APPLIES TO: This tutorial and the blower motor resistor in the images I'm using apply to the following vehicles:
- 3.0L V6 Nissan D21: 1990, 1991, 1992, 1993.
- 3.0L V6 Nissan Pathfinder: 1990, 1991, 1992, 1993, 1994, 1995.
- 3.0L V6 Nissan Pickup: 1994, 1995.
WIRING DIAGRAM: You can find the blower motor circuit diagram here: Blower Motor Circuit Diagram (1990-1995 Nissan Pathfinder And Pick Up).
NOTE: If you need to test the blower motor, see this tutorial: How To Test The Blower Motor (1990-1995 3.0L Pathfinder And Pick Up).
Blower Motor Resistor Basics
The blower motor resistor assembly is made up of 3 individual resistors. And as you're probably already aware, it's the blower motor resistor assembly's function to reduce the amount of current that passes thru' the blower motor.
This reduction in current makes possible several blower motor speeds.
To be a bit more specific:
- When the current is reduced by one resistor, the blower motor turns in LO speed.
- When the current is reduced by two resistors, the blower motor turns in Medium 1 (M1) speed.
- When the current is reduced by three resistors, the blower motor turns in Medium 2 (M2) speed.
- When the current is NOT reduced by any of the resistors, the blower motor turns in HI speed.
The resistors reduce the current that flows thru' them by converting it into heat. It's this heat that eventually will destroy the blower motor resistor assembly.
When the blower motor resistor assembly fails, you'll usually see one of the following symptoms:
- Blower motor works in high-speed only.
- Blower motor works in some speeds, but NOT all speeds.
It's very common for the resistor connector terminals to corrode or for the connector to burn and melt. This makes it very difficult to disconnect the electrical connector from the blower motor resistor assembly.
Another common problem is finding the resistor assembly coils corroded or burned out when removing the resistor assembly for testing.
TEST 1: Resistance Testing The Blower Motor Resistor
To test the blower motor resistor assembly we're gonna' test the resistance between its terminals with a multimeter in Ohms mode.
If the blower motor resistor assembly is bad then you're gonna' see a no-continuity test result from two of its terminals.
If continuity exists between all of its terminals then you can conclude that the blower motor resistor is good (not defective) on your 3.0L Nissan Pathfinder (D21 or Pick Up).
NOTE: To see actual resistance specifications for the continuity test of this test section, go here: Blower Resistor Continuity Specification Tables.
LOCATION: The blower motor resistor assembly is located behind the glove box. To access the blower motor resistor assembly you'll need to remove the glove box.
OK, let's get started:
Disconnect the blower motor resistor from its connector and remove it from its location.
Visually inspect the blower motor resistor assembly and connector for burn damage and severe corrosion.
If the blower resistor assembly and connector have any heat damage (in other words: burns or are melted), you can stop here and conclude they're bad and need to be replaced.
Place your multimeter in Ohms mode.
Check for continuity across two terminals at a time. Continuity should be present between all terminals.
NOTE: If continuity DOES NOT exist between 2 terminals, your multimeter will display the letters OL (Open Loop).
Let's take a look at what your test results mean:
CASE 1: Continuity exists between all the blower motor resistor terminals. This is the correct and expected test result.
You can conclude that the blower motor resistor assembly, on your 3.0L Nissan Pathfinder (D21 or Pick Up) is good.
CASE 2: Continuity DOES NOT exist between some of the blower motor resistor terminals. This test result tells you that the blower motor resistor is defective and needs to be replaced.
If the blower motor resistor's electrical connector is melted or is damaged, you'll need to replace it too.
You can find my recommendations, on where to buy the blower motor resistor assembly, here: Where To Buy The Blower Motor Resistor.