Blower Fan Motor Repair and Testing

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 the problem.

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 yourself.

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 information.

Tools and Supplies Needed

  • Replacement part
  • 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.

Step 1

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.

Step 2

Feel the flow of the air coming out of the vents if no air is felt then continue with this guide.

Step 3

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

Step 4

Locate the 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.

Step 5

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 removed easily.

Step 6

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. 

Step 7

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 as well.

Note: Intermittent power failure from the heater 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 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.

Learn more: How to check an electrical relay and wiring control circuit

Step 8

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.

Step 9

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.

Step 10

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.

Step 11

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.

Step 12

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.

Step 13

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.

Step 14

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.

Step 15

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.  

Step 16

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.

Step 17

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.

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