Is your heater or a/c blower motor not working and you want to fix it
yourself? With everyday tools while
getting an OEM factory replacement blower fan for a wholesale price from Amazon
(price that garages pay) you can save a considerable amount of money. When this
heater motor stops working one of three things has happened, either the
electrical supply has quit, the motor has burned out or the system ground has
failed. This guide will explain troubleshooting steps that will help you repair
I have created this guide to help you replace the part yourself in about an
hour using everyday tools and with a little instruction from us you can fix it
With no air coming out of the any of the vents for the defroster, air
conditioner or heater it can be uncomfortable and a little dangerous when you
cant see out of the windshield on a cold damp night. Plus there is nothing better
than knowing you didn't need to take the car in to a repair garage while
learning the valuable trade of fixing cars.
This motor is a normal service part because basically it's a high usage
electric motor that uses armature brushes that can fail in time. One of the
signs that the motor is going bad is when the system is on and the car hits a bump
and the motor start to work. This is telling you the brushes have worn out and
the blower needs replacing.
Before we get started, sit back and watch this video on how to replace
the unit first. This repair job is performed on a 2004 Mercedes Benz c230, then when
you are done watching read down the guide for additional
Tools and Supplies Needed
Basic tool set including Torx bits
Protective eyewear and gloves
Let's get started
It's best to begin by parking the automobile on level ground with the parking brake set.
With the key in the on position turn the fan switch to the high speed
setting, then to the medium and low speeds to test its performance.
Feel the flow of the air coming out of the vents if no air is felt then
continue with this guide.
The blower fan unitizes power from a
fuse or relay in the fuse panel. With the ignition key in the on position test
the fuse which can be identified by the fuse box cover or in the vehicles owners
manual, if the fuses are okay, proceed to next step.
Learn more: How to check a fuse in a car
motor which is usually under the dash or
hood on the passenger's side.
If your vehicles unit is located under the dash you must remove the lower cover
to gain access. Some manufactures are not kind when designing their systems and
can put the motor in a place where the heater box will need to be removed but
this is rare.
Once located (this particular motor is under the dash on the passenger's side) identify
the heater motor and the mounting screws holding it into the heater box. These screws
are mounted in the plastic housing and are not to terribly tight which can be
Next, locate and disconnect the a/c motor wiring by releasing the safety tab on the
side of the connector. This connector can have anywhere from one to four wires
depending if the system is a basic manually controlled unit, or an automatically
controlled climate system which varies the fan speed by using a solid state
speed rate controller apposed to a basic resistor.
Once dislodged, check the condition of the connecter and check for corrosion or
burned terminals which are a sign of high resistance or increased amperage draw.
If the connector is melted it must be replaced by splicing in a new part which
you can get from the dealer or Amazon.
It's best to solider these connectors to
cut down on resistance which helps the unit last longer opposed to crimp
connectors. This is due to resistance built up in the crimp connector compared
to the solider job which has minimal resistance.
Locate and disconnect the motor wiring connector. 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
Note: Intermittent power failure from the
fuse holder or
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 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.
How to check an electrical relay and wiring control circuit
Next, locate all mounting screws or bolts, some of these screws can be hidden
under metal braces, plastic tabs or wiring, use a small mirror if needed.
Start removing the mounting screws one at a time, the motor will then start
to fall out of the heater box, while holding it in place remove the last screw.
After all of the screws have been removed grasp the motor and remove it from the
housing, this can take some maneuvering so hang in there and be careful not to
damage the fan blade or (squirrel cage) against the heater plenum.
Once the old motor has been removed, compare
it to the new unit. In some cases an electronic speed controller
which is used in climate controlled systems will need to be transferred to the new motor but this is not typical.
On some less expensive replacement units you will need to transfer the old fan
blade over to the new assembly.
This is done by removing the mounting nut or
clip and then forcing the blade off of the motor shaft. Do not use oil or lube
of any kind to help installation of the fan onto the replacement motor because
it will allow the fan to slip on the shaft which will create problems.
To test the motor prepare a positive power and negative ground lead from a 12
volt power source (car battery). Use caution to not allow the clips to contact
each other or sparks (heat) will occur.
While grasping the motor firmly, attach
the power and negative wiring clips to the wiring harness. If the unit 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 wont confirming the motor
failure, these units typically fail intermittently.
Before installing the new motor into the plenum check for obvious obstructions
such as leaves, sticks, pens, tooth picks or small toys which have getting into
the system via the inlet or outlet vents. These foreign partials can keep the
motor from working freely and could cause premature failure.
When the new
assembly is ready to be installed fit the motor by maneuvering and rotating it gently, then push it back into the plenum
while lining up the mounting holes.
Once in place, start to install the mounting screws while holding the motor
toward the climate control plenum. Do not tighten any of the screws until all
screws have been threaded in by hand, this will make the installation go mush
easier without the potential for stripping the screws out or not getting some of
the screws threaded into the housing.
Tighten each screw in a
cross pattern, this will ensure the proper alignment of the fan blade in the
housing. If this step is not done properly it can cause the blade to contact the
housing creating a rubbing or clicking noise when the motor is operating.
After installing the new assembly, check the wiring connector locating tang
which indicates the orientation of the connector before it's installed onto the
motor. This tang is to ensure you don't install the connector incorrectly which
would cause electrical problems.
Then carefully re-insert the blower fan motor electrical connector by securing it into
position. You should hear an audible click telling you the connector is
installed correctly, gently tug on the wiring to ensure its correct
installation. Then reinstall the lower dash cover and install the mounting
screws by hand, then tighten snuggly but not to over tighten, again these screws
are going into plastic.
Next, start the engine up and turn the climate control on
and listen for the fan to come on. It should sound smooth and be blowing from
the vents in a strong flow. If you hear a rattle, squeak or ticking turn the
system off and remove the blower motor to recheck the installation.
If your vehicle is equipped with a cabin air filter it would be a good idea to
replace it at this time if you have not done it recently.
Learn More: how to replace an cabin air filter
Check out our blower fan forum if you have questions. Our community would love to help you. Most of us are mechanics by trade and will answer any question you might have.