If you suspect that the blower resistor has failed on your 1992, 1993, or 1994 3.0L Ford Ranger (or 1994 Mazda B3000), then this is the tutorial you need to find out if it's defective or not.
Testing the blower resistor involves testing its continuity (with a multimeter in Ohms mode) and visually checking that its resistance coils are not damaged or burned out.
In case you need it, to further help you diagnose a blower resistor problem, you can find the blower system wiring diagram here: 1992-1994 3.0L Ranger Blower Motor Circuit Diagram.
Contents of this tutorial at a glance:
NOTE: If you need to test the blower motor, see this tutorial: How To Test The Blower Motor (1992-1994 3.0L Ranger).
Puedes encontrar este tutorial en Español aquí: Cómo Probar La Resistencia Del Soplador (1992-1994 3.0L Ford Ranger) (en: autotecnico-online.com).
Blower Motor Resistor Basics
The blower resistor's job is to diminish the current passing thru' the blower motor so that you can get 3 different blower speeds (LO, M1, and M2). HI blower speed bypasses the blower resistor.
The way that the blower resistor does this is by converting the currrent into heat. And boy does the blower resistor get hot. This is the reason its located in the airstream of the blower motor.
Eventually, this heat will cause the blower resistor to fail and when it does, 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.
The cool thing is that testing it is a pretty simple affair on the 1992, 1993, and 1994 3.0L Ford Ranger.
TEST 1: Resistance Testing The Blower Motor Resistor
To get our Ford Ranger's blower resistor diagnostic on the road, we're gonna' test its continuity.
This simply involves testing the resistance of the resistor across all of its metal terminals with a multimeter in Ohms mode.
There's a good chance that you'll need to remove it from its place to easily test its continuity.
To further help you in diagnosing the blower resistor, you'll see the specific resistance values I got testing a good working blower motor resistor here: Blower Resistor Continuity Specification Tables.
NOTE: Don't have a multimeter and need to buy one? Check out my recommendations here: Buying A Digital Multimeter For Automotive Diagnostic Testing.
OK, let's get started with the test:
Disconnect the blower motor resistor from its connector and remove it from its location.
Visually inspect the blower motor resistor block and connector for burn damage and severe corrosion.
If the blower resistor block 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 analyze your blower resistor continuity test results:
CASE 1: Continuity exists between all terminals. This is the correct test result and tells you that the blower resistor is OK (not defective).
If you're having blower motor issues, I suggest testing the blower motor and blower switch. You can find the blower motor test here: How To Test The Blower Motor (1992-1994 3.0L Ranger).
CASE 2: Continuity DOES NOT exist between all terminals. This test result tells you that the blower resistor is defective and needs to be replaced.