Blower Motor Testing

Step by step guide on how to test an automotive blower motor for the air conditioner, heater and defroster modes. When the blower motor stops working one of three things had 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 repair the system.

This article pertains to all cars.

Difficulty Scale: 2 of 10

Tools and Supplies Needed

  • Test light
  • Protective eyewear and clothing
Begin by parking the automobile on level ground with the parking brake set.

Blower Motor
Step 1 - The blower motor unitizes power from a fuse in the PDC (power distribution center.) Visit - Fuse testing  If fuses are okay, proceed to next step.

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 - Fan motor work on high setting only  Using a test light connected to the negative side of the battery, probe both positive and negative wires for power. If one wire illuminates the test light, move the test light lead to the positive side of the battery and test the wire that did not illuminate the test light in the first test. If the wire illuminates the test light the blower motor has shorted and needs to be replaced. If both wires or neither wire illuminates proceed to next step. (Note: Sometimes a wiring schematic is needed to identify the ground or power wires.)

Step 3 - With the testing light connected to the positive side of the battery, test the ground wire. If the test light illuminates the circuit is okay, proceed to next step. If it does not light up the ground circuit has shorted and repair is needed.

Step 4 - Checking the power source of the circuit requires the test light to be grounded. Probe the power wire to the blower motor, if no illumination of the test light is observed and the system fuse is okay visit - Relay test  If tests okay proceed to next step.

Step 5 - For this test the climate control panel should be removed. Access the multi-speed fan control switch, Using a grounded test light probe each terminal as the switch is being activated form high to low speeds. One of the terminals should have continuous power, while the remainder of the terminals will illuminate the test light as the switch crosses the contacts internally (each speed). If no power is being distributed the switch has failed and needs replacement.

Best Practices

  • Use quality replacement parts to stem premature failure.
Article first published (Updated 2015-01-05)
Ask a Car Question. It's Free!
Need to replace the air cabin filter? Here is how it is done.