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Bad Blower Motor Symptoms Testing

Blower Motor Symptoms

To keep your car AC system in good condition, it’s essential to be on the lookout for bad blower motor symptoms. But how do you know if your blower motor is bad? That’s what we will be talking about in this section of the guide. Get to know what the most common symptoms of a bad blower motor are, their causes, and solutions. We will also be explaining how to test a blower motor before you can consider replacing it.

bad blower motor showing corroded parts
bad blower motor showing corroded parts

The Causes Of Bad Blower Motor Symptoms

Let’s start by looking at the causes of bad blower motor symptoms. A car blower motor develops problems due to:

  • Electrical problems such as faulty switch, blown fuse, damaged resistor or control module, bad relay (if it uses one), and corroded, melted, or loose connectors
  • Debris becoming lodged in the blower motor fan assembly
  • Worn motor parts such as brushes and bearing or burnt out motor components like coils and commutators

5 Common Bad Blower Motor Symptoms and their Meaning

A broken blower motor will show specific signs. These indicate a faulty part, which can be a switch, relay, fuse, fan or even the motor itself. If you understand what each symptom means, you can easily pinpoint (and fix) the affected component. Below are the most common bad blower motor symptoms.

Car AC Fan not working

No air comes out of the vents, even after switching on the AC. The blower motor not working can mean many things. It could be a bad motor or jammed fan wheel. It could also be a bad relay, fuse, or resistor. On a closer examination, you will also notice that the fan is not turning. Sometimes, the motor is working but the blower fan won’t rotate.

Unless the motor is burnt out, other problems can be fixed. You can replace a blown fuse or bad relay, for example. A bad blower motor resistor, too, or bad control module. Sometimes, it’s the wiring that’s damaged. In such cases, a proper diagnosis of the blower motor circuit is necessary to correct the fault. If the fan is jammed by debris, cleaning it is all that’s needed.

Blower Motor Blows Weak Airflow

The car AC fan slows down leading to a weak airflow and inadequate climate control in the cabin. The problem is usually the motor assembly, resistor, or the wiring. It means the motor is not receiving sufficient power, leading to reduced speed. It could also be that control module is faulty or the fan clogged with dirt and debris.

You can correct a damaged wiring system or bad resistor either replacing or repairing the faulty part. In cases where debris has accumulated in the fan assembly, removing the obstruction solves the problem. If left for longer, it could lead to a burnt out parts and the blower motor not working on any speed.

Blower Motor not working on all Speeds

Blower motor speed control is either by use of a set of resistors or control module. If your blower is resistor based, you may notice that it only works at the highest speed. This show the resistors are faulty, either from overheating or corrosion. Symptoms of a bad blower motor control module include a blower that will not operate at the required speed or one that shuts on and off.

When the blower motor has lost some of the speed settings, consider testing the resistors with a multimeter. The readings should match the blower motor specifications indicated in the manual. If your car uses an electronic module, its condition can be confirmed by the use of a scan tool, usually at a repair shop.

Car AC Fan Making Noise

This is one of the most common bad blower motor symptoms. The blower produces a rattling, screeching, or squeaking noise. A blower motor making noise can mean several things. It could be a worn motor, especially at the bearing or other moving parts. A noisy blower motor could also be caused by debris such as leaves getting lodged in the fan or blower assembly.

If the motor is worn, replace the entire assembly. You can also change the motor as a separate part depending on your type of blower. If debris is the reason for the reason for the AC blower motor making noise, you only need to clean it. We will be looking at the steps to clean the fan assembly later in the next chapter.

Smoke Coming out of Air Vents in Car

In the worst of situations, you may notice your car AC blowing smoke at the vents. This happens when the wires overheat and cause the insulation to melt. The smoke is also likely to be accompanied by the smell of something burning. Causes include short circuiting or a jammed fan that leads to current overloads as the motor strains to rotate.

Your car AC smoking at the vents is a dangerous situation that needs to be addressed immediately. If it happens while driving, quickly pull over and switch both the AC and engine off. If possible, have a mechanic check the car before you can use it again. The wiring would need a thorough inspection as well as the resistors and other electric parts of the system.

testing blower motor for voltage
testing blower motor for voltage

How to Test a Blower Motor

The blower motor runs a car’s AC system. Most climate control problems can be traced to it. Before deciding to repair or replace the blower assembly, you want to confirm if the motor is damaged. Testing blower motor assemblies involves measuring voltage at the connector and for different speed settings. Here is how to test a blower motor with a multimeter.

  • Access the blower motor. It’s usually located in the dash. Some vehicles will have it in the engine bay, so it’s a good idea to consult your manual
  • Find the connector. With the AC turned on and the multimeter set to the voltage scale, measure the voltage reaching the motor by connecting the multimeter probes to the connector pin.
  • Measure the voltage for both low and high blower speeds. You should get around 4 to 6 volts on low speed and 12 volts when the AC is at its highest speed. If there’s no voltage, it means the wiring is faulty or some of the components in the circuit such as relay, resistor, or relay are damaged. Proceed to test them.

Other Tests

If you notice bad blower motor relay symptoms such the car heater blower not working, you need to test the relay. For blower motor switch symptoms like the blower not working or only working on some speeds, consider checking the switch for damage. Most bad blower motor symptoms that involve speed problems are attributable to damaged resistors. Test them to confirm their condition. Below are the ways to test the various parts that are involved in the working of the blower motor.

Blower Motor Fuse Test

The fuse in most blower motors is located on the resistor pack. There’s also often another fuse on the dash. Check the fuse for damage using a digital multimeter. If it’s blown, there will be no electric power on one end and not the other. Replace it. If it’s functional, proceed to the other component.

Blower Motor Relay Test

Some blower motor circuits come equipped with a relay. The relay switches on power to the motor, allowing small currents to operate the circuit that connects the blower to the battery. Here is how to tell if blower motor relay is bad.

Locate the relay and place a finger on it. Switch the AC on and off. You should hear a click. Other relays require testing for power using a multimeter. In either case, a non-functional relay will be easy to diagnose. Replace it if faulty.

Blower Motor Resistor Test

Blower motor resistors are usually held in a resistor pack and installed somewhere near the blower itself, sometimes in the ducts. The resistors usually fail due to overheating or corrosion. You can tell a damaged resistor by looking or better still, by testing it with a multimeter. Here is how to check blower motor resistor for damage.

With the multimeter set to measure resistance, connect the probes to each resistor at a time. If the multimeter indicates an open circuit or infinite resistance, the resistor is damaged and need replacing. The resistance should also match the values indicated in the car repair manual

Blower Motor Control Module Test

If a blower motor does not use a resistor pack to control speed, it uses a control module. The module contains the electronics to regulate speed based on sensor signals. Just like the resistors, it’s also prone to damage by overheating and corrosion and leads to bad blower motor symptoms. The module requires a scan tool to diagnose.

Blower Motor Wiring Test

Connectors and cables can also cause blower motor systems. Check them by testing for power using a multimeter. You could also inspect the wiring using your eyes. Damaged cables or connectors are easy to diagnose by looking. Replace frayed cables, corroded connectors, or loose wire harnesses.


Bad blower motor symptoms indicate a failing or already failed HVAC system. Prompt action is then needed to restore the climate control of your car. The action can be either repair or replacement. Based on the type of problem, you may choose to repair the device instead. In the coming part of the guide, you will be learning how to fix a broken blower fan or in other words, car blower motor troubleshooting steps.

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