How To Test The Blower Motor (1987-1993 2.5L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma)

Are you having trouble with the blower motor in your 4.3L Chevy S10 pickup (GMC S15 pickup, GMC Sonoma)? If so, you've come to the right place.

In this helpful guide, you'll find the blower motor testing process explained step-by-step. You'll be able to diagnose and repair the problem in no time.

So, let's get started!

APPLIES TO: This tutorial applies to the following vehicles:

• 4.3L Chevrolet S10 Pickup: 1987, 1988, 1989, 1990, 1991, 1992, 1993.
• 4.3L GMC S15 Pickup: 1987, 1988, 1989, 1990.
• 4.3L GMC Sonoma: 1991, 1992, 1993.

Symptoms Of A Bad Blower Motor

The blower motor is an essential component of a heating and air conditioning system, and while it is designed to last for many years, it will eventually wear out and fail.

When it finally fails, you'll see one or more of the following symptoms:

• Blower motor doesn't work (at any speed you put the blower switch on).
• The blower motor speed is slow (even when on HI speed).
• The blower motor makes a lot of noise.

Blower Motor Circuit Descriptions

The blower motor, which can be found in the engine compartment, is connected to the vehicle's electrical system via a single spade connector.

The female connector that connects to this spade connector has a purple (PPL) wire. This wire provides the electrical current necessary to operate the blower motor.

It is important to note that the blower motor is grounded through a grounding strap that is attached to the metal frame of the motor. Without this grounding strap in place, the blower motor will not function.

Where To Buy The Blower Motor And Save

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

The following links will help you comparison shop for the AC Delco and after market blower motors:

TEST 1: Testing The Amperage Draw Of The Blower Motor

In order to determine if the blower motor is working properly, it's important to first check its electrical current draw.

The maximum allowable amperage for the blower motor is 25 amps. If it's drawing more than that, you can conclude that the blower motor is defective and needs to be replaced.

To measure the amount of current that the blower motor is drawing, we'll perform a resistance test using a multimeter.

Specifically, this test involves measuring the resistance of the blower motor, which is then used to calculate the current consumption using Ohm's law.

Let's get the ball rolling:

1. 1

   Disconnect the blower motor from its 1-wire connector.

2. 2

   Place your multimeter in Ohms mode.

3. 3

   Connect the red multimeter test lead to the blower motor male spade terminal of the 1-wire connector.

4. 4

   Connect the black multimeter test lead to a clean rust-free and unpainted surface on the blower motor body.

5. 5

   Take note of the resistance value your multimeter reports.

6. 6

   Divide 12.5 by the resistance value you got in the previous step.
   
   Let's say that you got a resistance reading of 0.4 Ohms in step 5. You would then do the following calculation: 12.5 ÷ 0.4 = 31.25. Which tells you that the blower motor has an amperage draw of 31.25 Amps.

Let's examine your test results:

CASE 1: Your test result shows the blower motor is using less than 25 amps. This is the correct and expected test result. With this test result you can conclude that the current draw of the blower motor is within specification.

The next test is to manually apply battery power and Ground to the blower motor. Go to: TEST 2: Applying 12 Volts To The Blower Motor.

CASE 2: Your test results shows that the blower motor is using 25 or more amps. This test result lets you know that the blower motor is defective and needs to be replaced.

TEST 2: Applying 12 Volts To The Blower Motor

For the second step in diagnosing the blower motor, we'll apply 12 Volts to the blower motor directly from the battery.

By applying 12 Volts directly to the blower motor from the battery, it should activate and run.

NOTE: For safety reasons, I recommend you use a 25 amp fuse protected jumper wire or a power probe to supply battery power to the blower motor.

NOTE: The blower motor does not need to be removed to test it. If you have already removed the blower motor and need to perform a bench test, you must Ground the metal frame of the blower motor or the test will not work.

Alright, these are the test steps:

1. 1

   Disconnect the purple wire from the blower motor.
   
   NOTE: Leave the black wire connector connected to the blower motor's case so the blower motor gets Ground.

2. 2

   Connect one end of your fused jumper wire to the battery positive (+) post.

3. 3

   Connect the other end of the fused jumper wire to the blower motor male spade terminal that connects to the PPL wire of the connector.

4. 4

   The blower motor should run without a metal to metal grinding sound.

Let's examine your test result:

CASE 1: The blower motor ran without any grinding noise. This is the correct and expected test result.

NOTE: If the blower motor is using more than 25 amps, even if it passed this test, it's bad and needs replacement.

CASE 2: The blower motor ran and made a loud grinding noise. This tells you that the blower motor has an internal problem (usually bad brushes or bearings).

Replace the blower motor with a new one.

CASE 3: The blower motor DID NOT run. This test result tells you that the blower motor is bad and needs to be replaced.

More 4.3L Chevy S10 Pickup, GMC S15 Pickup, And GMC Sonoma Tutorials

You can find a complete list of 4.3L Chevy S10 pickup, GMC S15 pickup, And GMC Sonoma tutorials here:

• S10, Sonoma 4.3L Index of Articles.

Here's a sample of the tutorials you'll find in the index:

• How To Test The Fuel Pump (1996-2003 4.3L V6 Chevrolet S10 Pickup, GMC Sonoma).
• How To Test The EGR Valve (1988-1995 4.3L TBI Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
• How To Test For A Blown Head Gasket (1988-2003 4.3L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
• How To Test Engine Compression (1988-2003 4.3L V6 Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).