Blower motor problems can cause many driver complaints. Anything from no air circulation to annoying or noisy operation. At the bottom of this page is a video that's very popular. It reviews best practices for diagnosing common problems. Finding the location of the fan assembly is a good place to start diagnosis.
The ac blower motor is usually located in the AC duct housing or heater case assembly. Usually this interior fan will be mounted near the evaporator and heater cores. Depending on the year, make, and model you may find this component both in the interior cabin area or outside in the engine compartment most often near the firewall.
You can use the component location diagram in your online service manual to pinpoint the specific location of the squirrel cage (fan blades). I can't tell you how often I have found a critter nest in the heater case! Location diagrams will also point out important parts in the climate control system such as relays, switches and fuses.
Be Careful! On some vehicles when the engine is running the interior fan is in constant operation at a low speed (astro ventilation). This is to provide an ample supply of fresh air in the interior compartment even when no climate control mode is selected. I believe General Motors first used it in the 70s.
On vehicles with early climate control systems the fans may not activate until the engine reaches a specific temperature. This is to prevent the circulation of ice-cold air on cold winter days when heat has been selected on the climate control.
Some drivers and car owners may complain about these normal operating conditions. You can not fix what is not broken. Its a good idea to check other like models to determine if there is a problem or is it just operating as per design intent.
Onto some common failures! The resister block on some models is coupled with a module and is used to control the output speed of the blower motor. Most typical resisters are connected to the motor in series. A resister block will adjust its total resistance as selected by the driver on the switch. As more resistance is applied to the circuit the slower the interior fan motor will spin.
In most cases with electrical problems I start at the load and work my way back through the circuit towards the battery. But when it comes to the interior fan I will usually go right for the fuse and check that first. Often there are 2 separate circuit fuses one under the dash usually a 20 amp. There can also be a 30 amp Maxi fuse in the engine bay panel.
With the amount of current and amps flowing through this circuit spikes can easily take out the fuse and damage relay's. If you do find a burnt fuse continue to test the system and 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 all the fuses and they are good, My next recommended step would be, continue diagnosis by using a test light or even better an automotive meter to verify good power and grounds at the blower motor.
I find often that DIY car mechanics will skip checking the ground and move right onto parts replacement mode if they find voltage to the fan motors. Remember, you need a good ground to complete the circuit. If my test light reveals no voltage at the fan and my fuse is good and a solid ground I move on.
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 with a solid ground present 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 when you remove the part you will instantly see that it has melted spots.
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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Learn how the rest of the climate control system works and discover why interior fans are an important part of the
automotive AC system.
You can learn more about this auto repair website over at the Homepage for YouFixCars.com.