How to test a fan motor with a multimeter

The fan motor resistor is responsible for pushing hot air through the vents whenever you turn on the heating system. The engine works hand in hand with your car's cooling and heating systems. If you notice strange sounds coming from the ventilation system, this means that the fan motor needs to be checked.

Performing fan motor maintenance with a multimeter will help you diagnose the component. Here I will take you through a detailed guide on how to test a fan motor with a multimeter.

Checking the Fan Motor with a Multimeter (5 Steps)

You can usually find the fan switch behind the glove box in your car. Once you find it, follow these steps to test the fan motor resistor:

Step 1: Test the negative wire with the positive lead of a multimeter.

The first task is to turn off the positive and negative charges of the power supply.

Usually the black wire is negative. But use the positive lead of the multimeter to test the black cable (negative) with the multimeter. Usually the black wire is negative. But use the positive lead of the multimeter to test the black cable (negative) with the multimeter.

Step 2: Turn on the engine

Start the engine using the ignition key to measure the current in the fan motor electrical connector (purple wire).

Step 3. Set the multimeter to DC power and measure

Switch the multimeter to DC power, then turn on the heater or air conditioner at maximum power.

Your fan switch is faulty if the multimeter shows no current/value. You should check the fan motor further if the multimeter detects current.

Step 4: Check if the relay is grounded

Now in the footwell, remove the fuse panel access cover, which you can find next to the side switch on the passenger side.

Remove the blower resistor relay from the vehicle. Check the relay if it is grounded or not using a multimeter (ohm scale). Then test it without grounding the current pin to the DC scale of the multimeter.

If you don't see any current, locate the IGN fuse under the cover, unscrew the cover panel, and connect the negative battery terminal to a multimeter. If the fuse is blown, I suggest you replace it.

Step 5: Check the connector

Check the connector to make sure the fuse is working. Turning on the ignition of the car and setting the multimeter to the DC scale, inspect the connector.

If everything works, then the relay should be replaced.

F.A.Q.

How to determine if a fan motor needs to be checked?

If you're having problems with your HVAC system, your fan resistor is definitely bad and needs to be replaced. Some of the warning signs of a bad fan motor include: (1)

Fan motor power is not working. If air does not pass through the vents when the air conditioner or heater is turned on, it may be broken. When your fan motor fails, there will be no airflow, requiring inspection or replacement.

The power consumption of the fan motor is minimal.

Your fan motor may be broken if the airflow in your vents is poor or non-existent. A weak or damaged fan motor will not be able to provide enough airflow to maintain a decent temperature.

Fan speed is low.

Another sign of a bad fan motor is that the motor only runs at a certain speed. Most fan motors are designed to run at a variety of speeds to adequately handle the varying temperatures in a home. If your fan motor is unable to deliver cold or warm air at the specified settings, this is a sign that it is defective. (2)

What are fan motors

1. Single speed motors

This type of motor blows air at a constant speed.

2. Variable speed motors

This motor blows air at different speeds.

Take a look at some of our articles below.

• How to test a capacitor with a multimeter
• How to measure DC voltage with a multimeter
• How to check the generator with a multimeter

Recommendations

(1) Hvac system - https://www.forbes.com/advisor/home-improvement/how-do-hvac-systems-work/

(2) speed - https://www.bbc.co.uk/bitesize/topics/z83rkqt/articles/zhbtng8