Blower Motor Relay Test (1991-1993 2.8L Chevrolet S10 Pickup, GMC Sonoma)

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

Four basic tests are involved in finding out if the blower motor relay is good or defective, and I'll explain them in a step-by-step way.

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.

APPLIES TO: This tutorial applies to the following vehicles:

• 2.8L Chevrolet S10 Pickup: 1991, 1992, 1993.
• 2.8L GMC Sonoma: 1991, 1992, 1993.

Symptoms Of A Defective Blower Motor Relay

When you move the blower speed switch lever to HI, the blower motor relay is activated and diverts the current going to the fan motor resistor assembly to the fan motor.

Since the current now bypasses the resistances of the blower motor resistor assembly, the blower motor gets full battery power and runs at HI speed.

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

Circuit Descriptions Of The Blower Motor Relay

The blower motor relay is located right next to the blower motor in the engine compartment. You'll also notice that its 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.

Where To Buy The Blower Motor Relay And Save

You can find the blower motor relay in any auto parts store. If you're wanting the buy the original AC Delco blower motor relay, you can buy it online for a whole lot cheaper than somewhere local.

The following links will help you comparison shop for the blower motor relay and hopefully save you a few bucks:

TEST 1: Making Sure The Blower Relay Is Getting 12 Volts

We're gonna start off by making sure that the blower motor relay is getting 10 to 12 Volts.

The connector terminal that delivers Ground to the relay is terminal E (see illustration above).

The battery voltage that terminal E provides is available 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

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

4. 4

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

5. 5

   Your multimeter should read 10 to 12 Volts.

Let's examine your test results:

CASE 1: Terminal E has 10 to 12 Volts present. This is the correct and expected test result.

The next step is to make sure the blower relay is getting Ground. Go to: TEST 2: Making Sure The Blower Relay Is Getting Ground.

CASE 2: 10 to 12 Volts are NOT present at terminal E. Without this voltage at terminal E the blower motor will not run in HI speed (when the relay gets the activation signal on terminal C).

The most likely cause of this missing battery voltage 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.