How To Test The Blower Motor Relay (1991, 1992, 1993 2.8L Chevy S10/ GMC S15)

This tutorial will help you to test the blower motor relay on the 1991, 1992, 1993 2.8L V6 Chevrolet S10 Pick-Up and S10 Blazer (GMS S15 pickup and Jimmy).

Two basic tests are involved in finding out if the blower motor relay is defective (or not) and I'll explain them in a step-by-step way.

En Español You can find this tutorial in Spanish here: Cómo Probar El Relé Del Motor Soplador (1991-1993 2.8L S10) (at: autotecnico-online.com).

NOTE: You can find the blower motor circuit diagram here: 1991-1993 2.8L Chevy S10 Blower Motor Circuit Diagram.

Symptoms Of A Defective Blower Motor Relay

The blower motor relay's job is to basically bypass the current that passes thru' blower motor resistor and deliver it directly to the blower motor. With the blower motor getting full battery current, it'll run in HI speed.

The most common symptom you'll see, when the blower motor relay fails in your Chevy S10 (GMC S15), is that the blower motor will not run in HI speed (but will run in LO, M1, and M2 speeds).

In some cases, the blower motor will fail and the blower motor will not run in HI but you'll have all of the other speeds working.

Circuit Descriptions Of The Blower Motor Relay

Circuit Descriptions Of The Blower Motor Relay. How To Test The Blower Motor Relay (1991, 1992, 1993 2.8L Chevy S10/ GMC S15)

The blower motor relay is located right next to the blower motor in the engine compartment. You'll also notice that it's connector has 5 wires coming out of its connector. Here's a brief description of each one:

Pin Wire Color Description
A BLK (black) Chassis Ground input.
B PPL (purple) Blower relay output to the blower motor.
C ORG (orange) Relay activation signal input (HI speed ON signal).
D DK BLU (dark blue) Stepped-down current input from blower resistor.
E RED (red) Battery power (+) input.

To further help you in diagnosing the blower relay (and its circuits), check out the blower motor circuit diagram here: 1991-1993 2.8L Chevy S10 Blower Motor Circuit Diagram.

TEST 1: Making Sure The Blower Relay Is Getting Power And Ground

How To Test The Blower Motor Relay (1991, 1992, 1993 2.8L Chevy S10/ GMC S15)

We're gonna' start off by making sure that the blower motor relay is getting power and Ground.

The specific connector terminals that we're gonna' test are: terminal A and terminal E of the blower motor's electrical connector.

Terminal A should have Ground all of the time, since this wire connects to your S10's chassis.

Terminal E should have battery power at all times.

WIRING DIAGRAM: You can consult the blower motor circuit diagram here: 1991-1993 2.8L Chevy S10 Blower Motor Circuit Diagram.

These are the test steps:

  1. 1

    Disconnect the blower motor relay from its electrical connector.

  2. 2

    Place your multimeter in Volts DC mode.

  3. 3

    Check that terminal A has Ground.

    A.) Probe terminal A with the black multimeter test lead. Terminal A connects to the black (BLK) wire of the blower relay connector.

    B.) Connect the red multimeter lead to the battery positive (+) post.

    C.) Your multimeter should read 10 to 12 Volts.

  4. 4

    Check that terminal E has 10 to 12 Volts DC.

    A.) Probe terminal E with the red multimeter test lead. Terminal E connects to the red (RED) wire of the blower relay connector.

    B.) Ground the black multimeter lead on the battery negative (-) post.

    C.) Your multimeter should read 10 to 12 Volts.

Let's examine your test results:

CASE 1: 10 to 12 Volts are present at both terminals. This is the correct and expected test result.

Now that you've checked the basics, the next step is to jumper terminals B and E together. For this test go to: TEST 2: Jumpering Connector Terminals B and E (HI Speed Circuit).

CASE 2: 10 to 12 Volts are NOT present at terminal A (Ground is missing). This test result tells you that the relay is not getting Ground.

Your next step is to repair the black (BLK) wire and restore its path to Ground.

CASE 3: 10 to 12 Volts are NOT present at terminal E. Without power at terminal E the blower motor will not get power to run in HI speed (when the relay gets the activation signal on terminal C).

The most likely cause of this missing battery power is an open in the red wire between the connector and the junction block where it connects to.

Your next step is to check the continuity of the red wire and restore battery power to it.