Testing the blower motor switch is a pretty simple thing to do since you don't have to remove it from the AC/Heater Control Panel to do it.
In this tutorial, I'll explain how to test it with a 12 Volt test light to see if its defective or not.
This tutorial applies to the 1998, 1999, and 2000 2.5L Ford Ranger (Mazda B2500) pickup truck.
Contents of this tutorial at a glance:
The following tutorials may come in handy:
- How To Test The Blower Resistor (1998-2000 2.5L Ford Ranger).
- How To Test The Blower Motor (1998-2001 2.5L Ford Ranger).
NOTE: You can find the blower motor circuit diagram here: Blower Motor Circuit Diagram (1998-2000 2.5L Ford Ranger).
Blower Motor Switch Basics
The blower motor switch (which is located on the AC/Heater Control Panel of your 2.5L Ford Ranger) is the one that lets you choose the blower motor speed.
Using the illustration above, these blower speeds are: LO, M1, M2, and HI.
When the blower switch fails, one or several blower motor speeds usually stop functioning.
In plain English, the blower motor's job is to channel the current passing through the blower motor resistor to a different circuit (wire) to achieve the reduction in the blower motor speed.
In a nutshell, this is what happens when you select a blower speed:
- When you select LO speed, the current is channeled through three resistor coils in the resistor block.
- When you select M1 (medium 1) speed, the current is channeled through 2 resistor coils in the resistor block.
- When you select M2 (medium 2) speed, the current is channeled through one resistor coil in the resistor block.
- When you select HI speed, the blower switch causes the current passing through the blower motor to completely bypass the blower resistor.
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 (1998-2000 2.5L Ford Ranger).
TEST 1: Testing The LO Blower Speed Circuit
The very first thing that we're gonna' do is to test the LO speed circuit.
If you've taken a look at the blower motor circuit diagram, you've probably noticed that the LO blower speed pretty much bypasses the blower switch.
The actual component that controls LO speed, is the vent control switch of the AC heater control panel.
The vent control switch also has a hand in the other blower speeds because it completes the path to ground that the blower motor needs to run.
To test the LO speed circuit (and the other 3), we're gonna' probe the blower resistor block's connector with a 12 Volt automotive test light (the photo above is of the blower resistor block electrical connector).
CIRCUIT DIAGRAM: Blower Motor Circuit Diagram (1998-2000 2.5L Ford Ranger).
These are the test steps:
Disconnect the blower resistor and the blower motor from their electrical connectors.
NOTE: This and all the other tests are done with the ignition key in its OFF position.
Place the AC/Heater Control Panel's vent selection control knob on any selection but OFF.
You can find the descriptions of the vent selections (of the vent control knob) here: Identifying The Vent Control Switch Selections.
Connect the 12 volt test light's alligator clip to the positive (+) battery terminal of your Ford Ranger's battery.
Select blower motor speed LO on the AC/Heater Control Panel.
Probe the female terminal identified with the #2, of the resistor block's connector, with the metallic point of your 12 volt test light (see photo above).
Female terminal #2 has a red with orange stripe (RED/ORG) wire connecting to it.
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 and lets you know that the AC/Heater Control Panel's vent control switch is working correctly.
Now that we've made sure that the vent control switch is working, we can test the other 3 speeds. The next test is to check that the M1 speed circuit inside the blower motor switch is functioning correctly. 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 AC/Heater Control Panel's vent control switch is defective. Replace the vent control switch.