How to Test an Automotive HVAC System Blower Fan Motor: A Detailed Guide

The following is a step by step guide on how to test a typical blower fan motor for the air conditioner, heater and defroster modes. When the blower motor stops working one of three things has happened, either the electrical supply has stopped, the motor has burned out or the system ground has failed. This guide will explain troubleshooting steps that will help you repair the problem. This article pertains to most cars.

Difficulty Scale: 4 of 10

Tools and Supplies Needed

• Test Light
• Basic Tool Set
• Protective Eye Wear and Clothing

Begin by parking the automobile on level ground with the parking brake set.

1. The blower motor unitizes power from a fuse or relay in the PDC (power distribution center). With the key in the "ON" position test the blower motor fuse which can be identified by the fuse box cover or in the vehicles owners manual. Visit - Fuse testing  If fuses are okay, proceed to next step.

2. With the key in the "ON" position turn the fan switch to the high speed setting, then to the medium and low speeds. If the fan motor works in the high speed setting only visit - Blower fan motor works on high setting only

3. Locate the blower fan motor which is usually under the dash or hood on the passengers side.

4. Locate and disconnect the blower motor wiring. Using a test light and a sharp metal object such as a hooked scribe to check for power at the connector (large wires). This test confirms power and the ground of the circuit, if the test light illuminates continue to the next step. This test can also be used by piercing the wiring harness as well.

Note: Intermitted power failure from the blower speed switch, fuse holder or climate control relay could be a problem so even though the circuit has power, its best to test the motor itself.

If the test light fails to light up, the ground or power circuit has shorted and a wiring schematic is needed to troubleshoot the problem further. If the blower motor only has one wire use a grounded test light for testing. Some vehicles are equipped with a blower motor relay which should also be checked. Please Visit - Relay Testing

5. Once power and ground have been confirmed, locate and remove the blower motor mounting bolts.

6. Once all mounting bolts have been removed grasp the blower motor and remove it for testing.

7. Prepare a positive power and negative ground lead from a 12 volt power source (car battery). Use caution as to not the allow the clips to contact each other or sparks (heat) will occur.

8. While grasping the motor firmly, attach the power and negative wiring clips to the blower motor wiring harness. If the blower motor only has a power lead attach the ground wire to the frame of the motor. Once the circuit is completed the motor will spin or will not confirming the blower motor failure. A blower motor typically fails intermittently, if the blower fan is not working and the vehicle hits a bump while driving and the blower starts up again the brushes inside the motor have worn out in most cases. Please Visit: Blower Fan Motor Failure Symptoms

Related Information

• Blower Fan Motor Not Working Questions
• Blower Motor Questions
• Replace Blower Fan Motor Questions
• Blend Door Actuator Replacement
• Heater Not Working
• Blower Fan Resistor Questions

Credits

This guide knowledge base was created by the 2CarPros Team, and by Ken Lavacot: Automobile repair shop owner and certified master automobile technician of over 30 years. If you have question or need help please ask one of our experts we are happy to help. Please visit our 2CarPros YouTube Channel.