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Get Accurate Results: How to Test Blower Motor with Multimeter

By shafiq usama

How-to-Test-Blower-Motor-with-Multimeter

As an electrical engineer, I love explaining how things like circuits and electronics work. I write on my blog to share simple explanations, reviews, and useful tips about the latest technology.

Many ask, how to test blower motor with multimeter? Learn about it in this blog!

It is always good to know how to test blower motor with multimeter. Simply, connect the power to the motor. Access the motor and locate the wiring. Set the multimeter to the resistance mode and connect the multimeter leads to the terminals. 

Check the multimeter reading for resistance. Compare the reading to the specified range provided by the manufacturer. If the reading falls outside the range, it may indicate a problem with the motor's windings.

What is a Blower Motor?

A blower motor is essential in various systems, including HVAC (Heating, Ventilation, and Air Conditioning) systems, automotive cooling systems, and other industrial applications. It is responsible for circulating air or coolant through the system, providing ventilation, heating, or cooling.

The blower motor is typically located within the air handler unit or furnace in HVAC systems. It draws air from the return ducts and forces it through the heating or cooling elements before distributing it into the living space through the supply ducts.

The blower motor is crucial in maintaining airflow and ensuring proper temperature regulation in residential, commercial, and industrial buildings.

Read more about How To Test Hvac Blower Motor With Multimeter?

How to Test Blower Motor with Multimeter?

Before proceeding, ensure you have the necessary safety equipment, such as safety glasses and gloves. Additionally, ensure that the power to the blower motor is disconnected to prevent any accidents. Here are the steps to know how to test blower motor with multimeter:

Step 1: Gather the Required Tools

To perform the test, you will need the following tools:

  • Multimeter (set to the resistance or ohms mode)
  • Safety glasses
  • Gloves (optional but recommended)

Step 2: Identify the Blower Motor

Locate the blower motor in your equipment or vehicle. It is usually located in the HVAC system, near the air vents, or behind the dashboard. Consult the equipment or vehicle's manual if unsure about the motor's location.

Step 3: Disconnect the Power

Ensure that the power to the blower motor is disconnected. This may involve turning off the equipment or disconnecting the battery for vehicles.

Step 4: Access the Blower Motor

Depending on the equipment or vehicle, you may need to remove some components or panels to access the blower motor. Follow the manufacturer's instructions or consult a repair manual for your equipment or vehicle to properly access the motor.

Step 5: Locate the Blower Motor Wiring

Once you have accessed the blower motor, locate the connected wiring. You should find a connector with multiple wires coming out of it. This connector is responsible for providing power to the blower motor.

Step 6: Inspect the Wiring

Inspect the wiring and connector for any signs of damage, such as loose wires, melted insulation, or burnt connectors. If you find any damage, it may indicate a problem with the blower motor or its wiring.

Step 7: Disconnect the Blower Motor

Disconnect the wiring connector from the blower motor. This will isolate the motor from the rest of the electrical system, allowing you to test it independently.

Read more about How to Test a Single-Phase Motor with a Multimeter

Step 8: Set the Multimeter

Set your multimeter to the resistance or ohms mode. If your multimeter has multiple resistance settings, choose the lowest one (typically labeled as "Rx1").

Step 9: Test the Motor Windings

Connect the test leads to the blower motor terminals with the multimeter set to the resistance mode. Ensure that the test leads connect securely with the terminals for accurate readings. The polarity (positive and negative) does not matter for this test.

Step 10: Interpret the Multimeter Reading

Check the multimeter display for the resistance reading. A typical blower motor should have a resistance reading within a specific range specified by the manufacturer. If the reading falls outside the specified range, it may indicate a problem with the motor's windings.

Step 11: Test for Continuity

In addition to checking resistance, you can test for continuity in the blower motor. Continuity testing helps identify any breaks or open circuits in the windings. To perform this test, set your multimeter to the continuity mode (often represented by a diode symbol). Then, place one test lead on each terminal of the blower motor.

Hearing a beep or seeing a reading close to zero indicates continuity, meaning the motor's windings are intact. If you do not hear a beep or the reading is infinite, it suggests a break in the windings.

Step 12: Repeat the Test (Optional)

If the resistance readings or continuity test results were outside the specified range, you may want to repeat the test to ensure accuracy. A poor connection or faulty multimeter settings can sometimes lead to incorrect readings.

Step 13: Reconnect the Blower Motor

After completing the test and verifying the results, reconnect the blower motor by attaching the wiring connector to its terminals.

Step 14: Reassemble the Equipment or Vehicle

If you had to disassemble any components or panels to access the blower motor, reassemble them following the manufacturer's instructions or repair manual.

Step 15: Reconnect the Power

Once you have reassembled everything, reconnect the power to the blower motor. This may involve turning on the equipment or connecting the vehicle's battery.

Following these steps, you can test a blower motor using a multimeter. Consider the equipment or vehicle's manual or seek professional assistance if you are unsure or uncomfortable performing the test yourself. Now, you know how to test blower motor with multimeter.

Signs and Symptoms of a Bad Car Blower Motor

There are many reasons for a faulty blower motor; here are the signs and symptoms that may indicate a faulty or bad car blower motor:

1. Lack of Airflow

One of the most apparent signs of a failing blower motor is a lack of airflow from the vents. If you notice a significant decrease in air from the vents, it could indicate a problem with the blower motor.

2. Intermittent Operation

A failing blower motor may exhibit intermittent operation. It might work fine for a while and then suddenly stop working. This irregular behavior can be a clear indication of a faulty motor.

3. Noisy Operation

A bad blower motor may produce unusual noises during operation. You may hear squeaking, grinding, or rattling sounds from the motor or the vents. These noises can be a sign of worn-out bearings or other internal issues.

4. Weak Airflow at Certain Speeds

If you experience weak airflow only at specific blower speed settings, it could point to a problem with the blower motor's resistor or control module. These components regulate the motor's speed, and a malfunction can reduce airflow in certain settings.

5. Motor Stuck at a Single Speed

A faulty blower motor may get stuck at a single speed and fail to respond to changes in the blower speed settings. 

6. Motor Doesn't Turn Off

A failing blower motor may not turn off even when the vehicle is switched off. It continues to run, leading to the draining of the vehicle's battery. A malfunctioning blower motor relay or control module could cause this issue.

7. Overheating Smell

How to Test Blower Motor with Multimeter

A failing blower motor may overheat, resulting in a distinct burning smell when used by the HVAC system. This smell can indicate a motor working harder than it should or potential electrical issues.

8. Blown Fuse

If the fuse for the blower motor repeatedly blows or needs replacement, it suggests an underlying problem. A short circuit in the motor or a wiring issue can cause excessive current flow, resulting in a blown fuse.

9. Electrical Issues

Another sign of a bad blower motor is electrical issues within the vehicle. This can include flickering dashboard lights, intermittent power loss, or other electrical malfunctions. These issues may indicate problems with the blower motor or its wiring connections.

Read more about How Often Does Electrical Wiring Need To Be Checked?

If you notice any of these signs or symptoms, you should have your blower motor inspected and potentially replaced by a qualified mechanic. Proper diagnosis and timely replacement of a faulty blower motor can help restore proper airflow and ensure optimal functioning of your vehicle's HVAC system.

FAQs

How do you diagnose a bad blower motor?

To diagnose a bad blower motor, check for lack of airflow, intermittent operation, unusual noises, weak airflow at certain speeds, a motor stuck at a single speed, motor not turning off, overheating smell, blown fuses, or electrical issues.

How do you check ohms on a blower motor?

To check the ohms on a blower motor, set your multimeter to the resistance mode, disconnect the motor, and connect the multimeter leads to the motor terminals. The reading will indicate the motor's resistance.

How many ohms should an HVAC blower motor have?

The ohms of an HVAC blower motor can vary depending on the motor's specifications. Refer to the manufacturer's documentation or consult a service manual to determine the acceptable resistance range specific to your HVAC blower motor.

Conclusion

You should know how to test blower motor with multimeter, as it is a straightforward process that can help determine its functionality. You can assess the motor's condition by following the steps, which include disconnecting the power, accessing the motor, setting the multimeter to the resistance mode, and checking the resistance reading. 

Comparing the reading to the specified range provided by the manufacturer allows you to identify any potential issues with the motor's windings. This test is an essential diagnostic step when troubleshooting HVAC, automotive cooling systems, or other applications that rely on a blower motor for proper airflow and temperature control.