Video: When Running the AC Should the Fan be on Auto or On: Optimizing Your AC Performance
Figure 1: Air conditioning outdoor units.
When your air conditioner's fan refuses to spin but emits a
distinctive hum, it can be a
frustrating and perplexing situation. However, there's no need to despair, as this issue is often fixable with some
troubleshooting and a basic understanding of your air conditioner's components.
In this article, we'll explore the most common reasons behind the "air conditioner fan not spinning but hums"
problem and how to diagnose and resolve each issue.
1. Most Possible Cause: Bad Fan Capacitor
One of the most common culprits behind an air conditioner fan that doesn't spin but hums is a faulty fan capacitor.
The capacitor is a crucial component responsible for kick-starting the fan motor, and when it fails, the fan can't
start properly. Fortunately, diagnosing and replacing a bad capacitor is relatively straightforward.
1.Inspect the Capacitor: Begin by visually inspecting the capacitor. It is usually a cylindrical
object located within the outdoor unit of your air conditioner. If you notice any signs of physical damage, such as
bulging or leaking, it's a clear indication that the capacitor is bad and needs to be replaced.
Figure 2: Air conditioner fan capacitor.
2.Discharge the Capacitor: Before attempting any repairs, it's essential to discharge the capacitor
to avoid electrical shocks. You can do this by using an insulated screwdriver with a plastic handle. Simply bridge
the two metal terminals on the capacitor to discharge any stored electrical energy.
3.Replacing the Capacitor: Once the capacitor is safely discharged, you can proceed to replace it.
Make sure to note down the capacitor's specifications, including its capacitance (measured in microfarads, µF) and
voltage rating.
Purchase a replacement capacitor with the same specifications, turn off the power to your air conditioner, and
carefully install the new capacitor in place of the old one.
4.Testing: After replacing the capacitor, restore power to your air conditioner and turn it on. If
the fan starts spinning, you've successfully resolved the issue. If not, it's time to explore other potential
causes.
Figure 3: Install a capacitor for an AC outdoor unit fan.
2. Other Possible Reasons for Air Conditioner Fan Not Spinning But Humming
If replacing the capacitor doesn't resolve the problem, there may be other underlying issues causing your air
conditioner fan to remain stationary while emitting a hum. Here are some additional factors to consider:
1.Damaged Motor:
A damaged fan motor can also prevent the fan from spinning. If the motor coil is damaged or the motor is stuck, the
fan won't rotate. To check for this, turn off the power to your air conditioner and attempt to spin the fan blade by
hand. If it doesn't rotate or resists movement, you likely have a motor problem. Replacing the motor may be
necessary.
2. Stuck Fan Bearings:
The fan bearings can become stuck due to foreign objects or become damaged over time. If the bearings are the issue,
the fan may be unable to rotate freely.
To fix this, you'll need to access the fan assembly, remove any debris, and lubricate or replace the bearings as
necessary.
3.Low Power Supply Voltage:
If your air conditioner is not receiving sufficient voltage, the fan may struggle to start. Check the power supply
and wiring to ensure that the voltage is within the recommended range. If the voltage is too low, consult a
professional electrician to address the electrical issues.
4.Poor Control Switch Contact:
The main control switch of your air conditioner can develop poor contacts over time, leading to erratic behavior. If
you suspect this is the issue, you may need to replace the control switch or have it serviced by a professional
technician.
Figure 4: Check the air conditioner outdoor unit fan.
3. FAQs
3.1 Why Air Conditioner Fan Not Working?
If the fan in the outside unit of an air conditioner is not working, it can indicate several potential issues. The
fan motor may be faulty, the capacitor that starts the motor could be defective, or there may be an electrical
problem.
When the fan doesn't operate, the outside unit may not be able to dissipate heat effectively, leading to reduced
cooling performance and potential damage to the compressor. It's crucial to address this issue promptly by
contacting a professional HVAC technician. They can diagnose the problem and perform the necessary repairs or
replacements to restore proper fan functionality.
Figure 5: Running air conditioning fan.
3.2 Why Air Conditioner Fan Keeps Running When Turned off?
If an air conditioner fan continues to run even when the unit is turned off, it could indicate a problem with the fan relay or control board. The fan relay or control board may
be stuck in the "on" position, causing the fan to keep running.
This issue can occur due to a malfunction or electrical problem within the control components of the air
conditioner. It is recommended to contact a qualified HVAC technician to diagnose and resolve the issue, as working
with electrical components can be dangerous. They will be able to identify the specific cause and make the necessary
repairs to rectify the problem.
3.3 Does Running the Fan on My Air Conditioner Use a Lot of Electricity?
Running the fan on your air conditioner typically consumes less electricity compared to running the compressor. However, it's worth noting that the exact energy consumption can vary depending on factors such as the fan speed setting, fan motor efficiency, and the specific model of your air conditioner.
3.4 Why Air Conditioner Fan Making Noise?
If an air conditioner fan is making noise, it could be due to several reasons. Common causes include debris or dirt
buildup in the fan blades, a loose or damaged fan blade, a worn-out motor bearing, or a faulty fan belt. The noise
can range from a rattling or buzzing sound to a squealing or grinding noise.
It is important to address the issue promptly to prevent further damage or complete fan failure. It is recommended
to turn off the air conditioner and contact a professional HVAC technician to inspect and diagnose the problem. They
can then perform the necessary repairs or replacements to resolve the noise issue.
Figure 6: Air conditioner outdoor units.
4. Conclusion
Dealing with an "air conditioner fan not spinning but hums" problem can be frustrating, but understanding the
potential causes and troubleshooting steps can help you identify and resolve the issue.
Start by checking the capacitor, as it's the most common culprit, and replace it if necessary. If the problem
persists, explore other potential reasons such as motor damage, fan bearings, loose set screws, power supply
voltage, and control switch contact.
In some cases, it may be best to seek professional HVAC assistance to ensure your air conditioner operates
efficiently and reliably, keeping your home comfortable during hot weather. Remember, safety should always be a
priority when working with electrical components, so exercise caution and turn off power to your unit before
attempting any repairs.
