Blower Motor Problems

Blower motor problems can cause many driver complaints. Anything from no air circulation to annoying noisy operation. Note: I put a video together that reviews best practices for diagnosing common problems near the bottom.

Finding the location of the fan/motor assembly is a good place to start your diagnosis.

The ac blower motor is usually located in the air-conditioning duct housing or heater case assembly. Often this interior fan will be mounted near the evaporator and heater cores.

Depending on the model, you may find the component both on the inside of the vehicle or the outside in the engine compartment area near the firewall.

Blower motor operation

On some vehicles when the engine is running the interior fan is in constant operation on its lowest speed setting.

This is to provide fresh air ventilation in the interior compartment, even when no climate control mode is selected.

General Motors used this back in the late 70s and called it astro ventilation. On vehicles with climate control, the fans may not activate until the engine reaches a predetermined temperature.

Some drivers and car owners may complain about this normal operation.

The resister block is used to control the output speed. The typical resister is connected to the motor itself in series.

The resister block will adjust its total resistance as selected by the driver. The more resistance applied to the circuit, the slower the fan will turn.

Blower motor common problems

The circuit fuse is usually a 20 amp yellow fuse but can also be a 30 amp green fuse. With the amount of current and amps flowing through this circuit, spikes can easily take out the fuse.

If you do find a burnt fuse continue to test the system to try to find out why it popped. Two common reasons for this to happen would be drawing too much amperage or a problem with the resister block mentioned above.

If you check the fuse and it is good. My next step would be to continue by using a test light to verify good power and ground at the blower motor itself.

Often diy car mechanics will skip checking the ground and move right onto parts replacement mode if they find voltage to the fan motors. Remember that you need a good ground to complete the circuit.

If my test light reveals no voltage at the fan and my fuse is good. I will usually head to the resister block assembly and check for power coming out on the resister itself.

If your test reveals power going in to the resister and nothing coming out this is most likely your failed component.

The resister block is also usually mounted in the air conditioner or heater case. And in most cases, not far from the squirrel cage itself for cooling purposes. If you have no power coming out you can remove this component and visually inspect it.

Often when this component fails, catastrophic heat related failure occurs. This means that when you remove the part you will instantly see that it is a melted. Example image on the left.

Fixing your own problems in this system is usually well within reach for the average do-it-yourself mechanic. The diagnostic charts provided in car repair manuals are usually very basic and do not require any special tools. "Example video below"

The replacement of the parts in the system is also usually some of the easier repairs to perform on the automobile. There are a few vehicles out there that do make this extremely difficult. You will have to decide on your own if this is within your skill level.


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