How to Test a Blower Motor with a Multimeter

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How to Test a Blower Motor with a Multimeter

In every home or vehicle, an HVAC system is a must-have. With changing seasons, from summer to winter, an HVAC system is the most depended on the device.

In every HVAC system, there is a component known as a blower motor. This blower motor is responsible for blowing heated air through your vents when the heating system is on. The motor is also responsible for blowing cold air through your vents.

​Types of blower motors

1. single-speed motors

This type of motor blows air at a constant speed.

2. variable-speed motors.

This motor blows air at varying speed levels.

With the need to maintain comfortable temperatures within your home or vehicle, the HVAC is a vital component to have.

How does a blower motor work?

The motor works together with your home’s cooling and heating system; a thermostat monitors your home temperatures.

When the temperature falls below your thermostat setting, it sends signals to the furnace, which in turn starts to work. The furnace works by creating cold or hot air, which circulates to various rooms in your home.

The blower is responsible for circulating the cold or hot air created by the furnace throughout your house to ensure your temperature reaches the thermostat. The blow motor makes this possible by spinning a fan.

The fan, in turn, blows the cold or heated air through your ventilation system. The small-sized blower motor can move large air volumes. The thermostat is also responsible for communicating to your HVAC’s blower motor to either turn it on or off.

Between the single speed and the variable-speed motors, the best type of blow motor preferred is the variable-speed motor. The single-speed motor always resorts to cold sports as it only works when signaled by the thermostat.

The variable-speed motor, on the other hand, maintains comfortable temperatures throughout as it blows cool or heated air at varying speeds.

How to know your blower motor needs testing?

If you experience some of these problems with your HVAC system, it can only mean your blower motor is faulty and may need testing. Some of the symptoms of a defective blower motor are:

1. if there is no air coming out of your vents

If you are not experiencing air from your vents when the air condition or the heated system is on, it might be faulty. When your blower motor is faulty, then it means no air will be circulated, and thus the need for testing or replacement.

2. If you experience Weak airflow coming from your vents

If you experience weak or less airflow in your vents, then this can mean your blower motor is failing. A weakened or faulty blower motor cannot create enough airflow to regulate your cabin’s temperature.

3. Reduced fan speed

Another symptom to identify a broken blower motor is if the motor functions at only a certain speed. The majority of blower motors are created to work at different speeds to regulate different house temperatures correctly. If your blower motor is unable to push cold or heated air at its designed settings, it means it’s faulty.

If you are experiencing some of these signs, you need to…

​Test Your Blower Motor

Tools needed… a Multimeter

What is a multimeter?

A volt-ohm meter or commonly known as a multimeter is a tester that measures electrical, current, voltage, resistance, and other values.

There are two types of multimeters:

1. Analog multimeter
2. Digital multimeter
  • This type of multimeter is the most preferred by many.
  • Though expensive, it’s easy to use and gives accurate readings.
  • Unlike the analog multimeter’s needle and graduate scale, this device has an LCD screen.
  • The digital multimeter is the most preferred type of multimeter due to its high digital resistance. Once you are equipped with a multimeter, preferably a digital one, then you can begin testing your ignition coil.

​There are t​wo types of digital multimeters:

Fluke digital multimeter

The multimeter is mostly used to calibrate voltage usage and resistance in your home’s machinery. It is highly recommended for anyone not sure which digital multimeter to use. It is the ideal tool for armatures.

Clamp digital multimeter

Measures electrical flow using in-build tools.

With the ability to measure: Flow of Electricity, Voltage, Power Consumption, Wattage, and Amps, this device is recommended for professionals.

How do you test a blower motor using a multimeter?

Before you start performing any test, it is advisable to first:

1. Check the Power.

When your electrical devices are completely failing, the first thing to do is to make sure they are accessing incoming power.

2. Check for debris

If the power is incoming, but your blower motor is still not functioning, your next step should involve taking off the cover panels to look at the motor directly. If there is debris, then this is a symptom that your motor has a short. Cleaning the motor can make it function again.

Testing the blower motor of your vehicle using a multimeter

The blower motor in your car is usually located behind your vehicle’s glove compartment. Disconnecting the positive and negative power supply is the first thing to do.

The black wire is normally negative. With your multimeter (Ohm scale), you need to take the positive lead of the multimeter to test the negative black cable.

  1. Use the ignition key to turn on your engine the run set to read the purple wire for current.
  2. Next, having set your multimeter to DC power, turn either your heater or cooling energy to full strength.
  3. When your multimeter reads no current, then your blower motor is defective.
  4. If the multimeter identifies a current, then further testing of the blower motor is needed.
  5. The next thing is to remove the cover of the fuse panel access, located next to the shifter of the passenger’s side in the footwell.
  6. ​Take out the car’s blower motor relay. Read the grounded relay with your multimeter (Ohm scale). Then check the current pin while not grounding it to the multimeter’s DC scale.
  7. If you don’t read any current, check the junction box under the hood for the IGN fuse, remove the cover panel, and using a multimeter, connect it with the negative side of your battery. If its fuse is broken, then replacing it is advised.
  8. If its fuse works, then check its connector. With your car’s ignition on the run, using the multimeter on the DC scale, test the connector. Check the fuse using a multimeter.
  9. If everything works, then you need to replace the relay. When you replace anything that isn’t working, the blower motor should start working.

Testing the blower motor of your home HVAC system

If debris is not the problem, use your multimeter to check for voltage in the contacts motor. The resistance (ohms) of the windings should be tested. If it’s a zero reading, then this indicates that your winding has a shortage. If it reads an infinity symbol, then it means the winding has an opening somewhere.

Check the Capacitor.

Next, move to its capacitor. The capacitor generates typically the torque needed by the motor. You are likely to find it connected to two brown wires running from the motor.

Make sure the unit power is turned off. Next, you discharge the capacitor before testing. The simplest way to test the capacitor is by use of a specialized-capacitor testing tool. If you are not equipped with it, then check the resistance by use of the multimeter. You need to connect a lead to each terminal. After this, you should notice the readings start from zero.

About the Author Dan

Just a random guy who likes to build things. Providing tool knowledge, appliance/device testing tips, and DIY project info in an easy-to read & non-intimidating style.