Testing the blower motor on the 1995, 1996, and 1997 3.0L Ford Ranger (Mazda B3000) involves two easy and simple tests.
The first one is an amperage draw test and the other one involves applying battery power and Ground to it to see if it runs.
Both can be done easily by the DIY'er at home and in this tutorial you'll find them both explained in a step-by-step way.
Contents of this tutorial at a glance:
NOTE: If you need to test the blower motor resistor, see this tutorial: How To Test The Blower Motor Resistor (1995-1997 3.0L Ford Ranger).
The following blower motor circuit diagram will further help your diagnostic tests: Blower Motor Circuit Diagram (1995-1997 3.0L Ford Ranger).
Blower Motor Basics
In a nutshell, the blower motor is a two wire component that needs power and Ground to run (which makes it super easy to test). One wire is the wire that feeds it power and the other is the Ground wire (you can see the circuit diagram here: Blower Motor Circuit Diagram (1995-1997 3.0L Ford Ranger)).
Now, when the blower motor fails in your Ford Ranger, you're gonna' see one of the following symptoms:
- The blower motor will stop working completely.
- The blower motor will run, but run with a lot of bearing noise.
It's common for the blower motor's bearings to wear out. When this happens, it'll run with a lot of noise. What stinks about this (besides the noise) is that because the bearings are worn out, the blower motor will use an extreme amount of current (from the mechanical resistance to the motor rotation). This high amperage draw can overheat and destroy the blower motor resistor.
TEST 1: Testing The Amperage Draw Of The Blower Motor
We're gonna' start the blower motor diagnostic by testing its amperage draw. All you'll need for this test is a multimeter.
Once you get the resistance (Ohms) value of the blower motor and then we'll use Ohm's Law to calculate its amperage draw (Ohms Law: Amps=Volts ÷ Ohms).
If the amperage draw is above 40 Amps, then you can consider the blower motor defective and in need of replacement.
NOTE: If you don't have a multimeter and need to buy one, check out my recommendations here: Buying A Digital Multimeter For Automotive Diagnostic Testing.
Let's get started:
Disconnect the blower motor from its electrical connector.
Place your multimeter in Ohms mode.
Measure the resistance of the blower motor with your multimeter. You'll be testing across the blower motor's connector and not the vehicle's wiring harness connector.
Divide 12.5 by the resistance value you got in step 3 (12.5 is the battery voltage value). The result of this calculation is the amount of amperage the blower motor is using.
To be a little more specific: Let's say that the resistance reading was 0.4 Ohms. This is what the math would look like: 12.5 ÷ 0.4 = 31.25 and this would translate to 31.25 Amps.
Let's take a look at your test results:
CASE 1: Your test result resulted in a calculation of under 40 Amps. This is the correct and expected test result and let's you know that the blower motor amperage draw is within specification.
The next step is to manually apply power and Ground to the blower motor itself. For this test go to: TEST 2: Applying Power And Ground To The Blower Motor.
CASE 2: Your test result resulted in a calculation of 40 Amps or more. This test result tells you that the blower motor, on your Ford Ranger or Mazda B3000, is defective and needs to be replaced.
Here's why: This high amperage draw is the result of worn out bearings causing a tremendous amount of friction to the rotation of the blower's fan shaft. To overcome this friction, the blower motor needs more current to turn. This higher current will eventually fry the blower resistor or the blower switch.