How To Test The Blower Motor Switch (2.8L Chevy S10/ GMC S15)

The blower motor control switch, on your Chevrolet S10 (GMC S15) can be easily tested to find out if it's bad (or not). In this tutorial, I'll show you two different ways of doing this.

Contents of this tutorial at a quick glance:

  1. Basics Of Troubleshooting The Blower Control Switch.
  2. TEST 1: Checking Continuity Of The Blower Switch Fan Speeds.
  3. TEST 2: Making Sure The Blower Switch Is Getting Power.
  4. TEST 3: Using a Jumper Wire To Bypass The Blower Switch.
  5. Where To Buy The Blower Switch And Save.
  6. More GM 2.8L Tutorials.

En Español Puedes encontrar este tutorial en Español aquí: Cómo Probar El Interruptor Del Motor Del Soplador (2.8L V6 GM) (en: autotecnico-online.com).

The following tutorials may also come in handy (and compliment this one):

  1. How to Test The Blower Resistor (2.8L Chevy S10/GMC S15).
  2. How to Test The Blower Motor (2.8L Chevy S10/ GMC S15).

Basics Of Troubleshooting The Blower Control Switch

How To Test The Blower Motor Switch (2.8L Chevy S10/ GMC S15)

At it's most fundamental level, the blower control switch simply diverts the incoming current to one of three circuits. Which circuit the current is diverted to depends on what blower speed you have moved the lever to.

To be even more specific: The blower switch mechanically opens and closes a set of contacts (within) to divert the incoming battery power from the BRN wire to any of the other three wires as you move the blower control switch lever to any of the blower speed positions (LO, M1, M2, or HI).

Here's a further breakdown of how the blower switch does what it does:

  1. When the blower switch lever is in the LO position:
    1. Battery power is available in terminal D of the blower switch connector.
    2. The blower switch does not channel this current anywhere.
    3. The blower motor runs in LO speed.
  2. When you move the blower switch lever to the M1 position:
    1. Battery power is available in terminal D of the blower switch connector.
    2. The blower switch closes circuits D and A and channels the incoming battery power to the TAN wire of the blower switch connector.
    3. The blower motor now runs in M1 speed.
  3. When you move the blower switch lever to the M2 position:
    1. Battery power is available in terminal D of the blower switch connector.
    2. The blower switch opens circuits D and A.
    3. The blower switch closes circuits D and C and channels the incoming battery power to the LT BLU wire of the blower switch connector.
    4. The blower motor now runs in M2 speed.
  4. This interruption and diverting of battery power goes on for all of the other blower fan speeds.

Since these are mechanical connections the blower switch is making to open and close these circuits... over time and use these contacts become pitted and covered in carbon (from the electrical arching that occurs when the contacts close). When this happens, one or several of the blower fan speeds stop working.

The cool thing is that diagnosing/troubleshooting the blower switch isn't hard. The following circuit descriptions will help:

Blower Switch Circuit Descriptions
Pin Wire Color Description
A LT BLU M2 Speed Output.
B TAN M1 Speed Output.
C YEL LO Speed Output.
D DK GRN OFF Output.
E -- Empty
F -- Empty
G BRN Battery Power From Fuse.
H LT BLU M2 Input from AC-Heater Panel

NOTE: There's a good chance that the color of the wires described above DOES NOT match what's on your particular vehicle. This is no cause for concern since the circuit descriptions are the same for all of the GM vehicles covered by this repair tutorial.

TEST 1: Checking Continuity Of The Blower Switch Fan Speeds

How To Test The Blower Motor Switch (2.8L Chevy S10/ GMC S15)

The very first thing we'll do, to see if the blower switch is fried or not on your Chevy S10 (GMC S15), is to do a few simple continuity tests with your multimeter in Ohms () mode.

You'll need to unbolt and pull the AC/Heater Control Panel (but not completely remove it) from its location on the instrument panel... so that you can access the blower switch terminals (see the photo below).

OK, these are the test steps:

  1. 1

    Unbolt and pull the A/C-Heater control panel from the dash. You'll only need to pull it out far enough to access the blower motor switch and unplug it from its connector.

    Set your multimeter's dial to Ohms mode ().

  2. 2

    Disconnect the blower switch from its electrical connector. All the continuity tests, in this test section, are done on the male spade terminales of the switch itself.

  3. 3

    With the blower switch lever set to the M1 position.

    You should have continuity between D and A.

  4. 4

    With the blower switch knob set to the M2 position.

    You should have continuity between D and C.

  5. 5

    With the blower switch knob set to the HI position.

    You should have continuity between D and B.

Let's take a look at what your test results mean:

CASE 1: One or more of the circuits tested DID NOT have continuity in the indicated blower switch lever position indicated. Repeat the tests just to make sure of your test results.

If continuity is not present where indicated in the test steps above and this lack of continuity coincides with the blower fan speed that's not working on your S10/S15 pick-up or SUV... then you've found the cause of the problem.

Replace the blower switch in the A/C-Heater control panel with a new one to solve the problem. To comparison shop for the blower control switch, take a look at this section here: Where To Buy The Blower Switch And Save.

CASE 2: All circuits tested had continuity where indicated in the test steps. This is good and is the correct and expected test result that tells you that the blower fan switch (in the A/C-Heater control panel) is OK.

Your next step is to bypass the blower switch using a simple jumper wire. For this test go to: TEST 2: Making Sure The Blower Switch Is Getting Power.

How To Test The Blower Motor Switch (2.8L Chevy S10/ GMC S15)