The blower motor is one of the easiest components to check on your 2.5L Chevy S10 pickup (GMC S15 pickup, GMC Sonoma).
In this tutorial, I'll walk you through the testing process step-by-step. With your test results, you'll quickly determine if the blower motor is good or bad.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar El Motor Del Soplador (1987-1993 2.5L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles:
- 2.5L Chevrolet S10 Pickup: 1987, 1988, 1989, 1990, 1991, 1992, 1993.
- 2.5L GMC S15 Pickup: 1987, 1988, 1989, 1990.
- 2.5L GMC Sonoma: 1991, 1992, 1993.
NOTE: The following tutorials will help you test the blower motor resistor and blower motor speed switch:
- How To Test The Blower Motor Resistor (1988-1993 2.5L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
- Blower Motor Speed Switch Tests (1987-1993 2.5L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
Symptoms Of A Bad Blower Motor
When the blower motor 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.
The focus of this tutorial diagnosing a 'no blower' condition.
Blower Motor Circuit Descriptions
The blower motor is located in the engine compartment and you'll notice that it has only one electrical connector.
The wire that connects to the blower's single spade connector is a purple (PPL) wire that supplies electrical current to the blower motor.
FYI: The blower motor is grounded via a grounding strap connected to the metal frame of the blower motor.
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
To check if the blower motor is defective, we must first check the electrical current (amperage) it's using.
Twenty-five amps is the maximum amount of amperage that the blower motor can use. Any amperage use above 25 amps, you can conclude the blower motor is bad and needs to be replaced.
Now in case you're wondering, a simple multimeter resistance test is performed to determine how much current the blower motor draws.
The resistance value is then used to determine the current used by the blower motor using Ohm's law.
These are the test steps:
Disconnect the blower motor from its 1-wire connector.
Place your multimeter in Ohms mode.
Connect the red multimeter test lead to the blower motor male spade terminal of the 1-wire connector.
Connect the black multimeter test lead to a clean rust-free and unpainted surface on the blower motor body.
Take note of the resistance value your multimeter reports.
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 our second test, we'll apply 12 Volts from the battery to the blower motor.
The expected test result is for the blower motor to activate when it receives 12 Volts from the battery.
NOTE: As a safety precaution, use a 25 amp fused jumper wire or a power probe to provide 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:
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.
Connect one end of your fused jumper wire to the battery positive (+) post.
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.
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 2.5L Chevy S10 Pickup, GMC S15 Pickup, And GMC Sonoma Tutorials
You can find a complete list of 2.5L Chevy S10 pickup, GMC S15 pickup, And GMC Sonoma tutorials here:
Here's a sample of the tutorials you'll find in the index:
- How To Test Engine Compression (1985-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma).
- How To Test For A Blown Head Gasket (1985-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma).
- How To Test The TPS (1987-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma).
- How To Test The MAP Sensor (1985-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma).
If this info really saved the day, buy me a beer!