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
Protective eyewear and clothing
Begin by parking the automobile on level ground with the parking brake set.
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.
Use quality replacement parts to stem premature failure.
Written by Ken Lavacot Co-Founder and CEO of 2CarPros.com 35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.
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Article first published 2013-08-19 (Updated 2015-01-05)