Loud noises coming from your AC unit when it turns on can be caused by a variety of issues — electrical shortages, failing fan motors, broken fan blades, clogged filters, and more. You might be able to fix a few of these issues yourself, but in most cases, you’ll have to hire an HVAC technician to diagnose and fix the cause.
Any time you hear strange sounds coming from your air conditioner unit, it can instantly invoke anxiety, especially during the hot summer months or when you have a high-risk person living in your home. This guide will help you troubleshoot the sound and provide some tips for identifying and fixing common AC problems, too.
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What are the Most Common Causes of Loud Noises Coming From Your HVAC?
Air conditioning systems are complex and they have several components that work together to remove heat from your home and cool it. Air conditioner noise can be normal, but all of those parts can wear on each other, and when one or more component gives, your unit can begin making some pretty awful sounds.
There is a plus side, by listening closely to the sound your unit is making, you may be able to diagnose the issue without having to pay an expensive service bill.
Rattling Noises and Humming Noises
Loose parts can make a rattling or humming sound. Due to the vibration in your AC unit, it is not uncommon for parts to come loose.
However, you should fix loose parts as soon as you notice them. Otherwise, they may damage other components turning a simple DIY fix into a costly HVAC repair.
Squealing Noises and Buzzing Noise
Anytime you hear buzzing coming from an electric-powered appliance, it could be a sign of serious electrical problems. Your air conditioner usually makes this sound when the voltage is too low, wires have come unsoldered, your compressor motor is failing, or you have a bad capacitor, you may hear a buzzing noise coming from your air conditioner.
An improperly seated air filter can also cause a rattling sound inside when you start up your unit or power it off.
Banging Sounds and Slamming Noises in Your House
A slamming sound or banging noise, clanking, or clanging, could be your AC system’s damper closing when your system shuts off. The sound is usually very brief and it may sound like two pieces of sheet metal clashing together.
A Clanking Noise in Your Air Vent
If the blower motor connected to your heat pump is no good, you may hear a light thud or clanking coming from your air vent. The noise you hear could be a result of the blower wheel hitting another component or something foreign in your HVAC.
Cracking and Creaking Sounds Coming From Ductwork
When your air conditioner turns on and shuts off, it is not uncommon for airflow or pressure to make the ductwork and other flexible parts creak and crack. Cracking sounds are usually nothing to concern yourself with unless you hear a crack followed by a thud.
The air ducts and other flexible components may also creak and crack as the temperature changes. While it is not an incredibly loud sound, it can be startling because it sounds like your building is cracking.
Your Air Conditioner Makes Clicking Noises
Like buzzing and humming, a clicking noise either when the system is on or off could mean you have a major electrical issue. The unit clicks because it is attempting to turn on.
To avoid calling an HVAC technician for a simple fix, make sure that none of the breakers are tripped. If a circuit is tripped, at least part of the unit will not be functioning.
Related: AC Pulsating Noise
What Should You Do If You Hear a Loud Noise Coming From Your AC?
A loud noise coming from your outside unit means you likely have a broken compressor, run capacitor, or condenser fan motor. Each of those components is vital.
If one or more is not functioning, it will cause warm air to come out of your air vents, and if you leave the components unfixed, they could compromise other parts, too. So, here are a few steps you can take to troubleshoot and fix a noisy air conditioning unit.
1. Check the Outdoor Fan and Inspect the Unit
Your condenser fan is the giant blades that are in the center of your outside unit. Before you adjust the thermostat or start troubleshooting, you should check to see if the fan is rotating, and if it is, observe how the blades are spinning.
If they seem to be off-balanced or you hear the fan hitting something, debris in the condenser casing could be responsible for the sound you hear. If you do not see anything hitting the fan, check to see if the coil appears to be in good condition, and check the copper refrigerant piping at the base of the unit for ice.
If there is ice on your unit, it means your HVAC system freon levels are low and there is likely a refrigerant leak. In this case, you’ll need to hire an HVAC pro to fix the leak and recharge the refrigerant.
2. Change Your Air Filters
Clogged air filters can wreak havoc on your HVAC system. With a dirty AC filter, even if your blower, air intake, compressor, and other crucial central air components are in good condition, your HVAC will struggle to maintain a comfortable temperature in your home and they can also create humming or rattling noises.
3. Clean Your Outdoor Unit
Because the sound you hear could be something hitting the condenser fan, it is a good idea to clean the outside unit. Before you begin, turn your AC off and turn the power off to the condenser by locating the breaker box near your air conditioner unit.
Once you locate the box, make sure that the switch is off, that way if someone else turns the AC on while you are working on it, the fan will not start spinning.
When it is safe, remove the top grille and carefully take out anything that has fallen inside. Then carefully remove any buildup on your coil. If the coil is dirty, you can use an AC coil cleaner to remove caked-on dirt and grime.
3. Check the Run Capacitor
If the fan was not rotating when you first checked, see if it works when you turn your air conditioner back on. If it does not, you can try to jumpstart it by using a tool to gently push the blade after you set your thermostat to at least 10 degrees below your home’s temperature and switch the AC to ‘on.’
If the fan starts spinning the problem is likely a run capacitor, which is the part responsible for signaling the fan to come on.
If you rule out the fan motor, condenser coil, fan blades, and run capacitor and you are still hearing the noise, it is likely your compressor.
4. Inspect Your Indoor Air Handler
If you are unable to identify a problem with your outside AC unit, you need to move to the indoor unit. When you are inspecting the air handler, look for visible signs of a problem, like bent coil fins or ice and buildup on the evaporator coil.
You might want to explore HVAC home warranty subscriptions that provide protection for expenses related to AC repairs or the replacement of malfunctioning AC components.
For more information on why your air conditioner is making loud noises, check out this video:
Final Advice When Your AC Makes a Loud Noise When Starting Or Shutting Down
Under normal operation, your air conditioner should not make any concerning sounds. When it does, it means your system is likely breaking down. Short of replacing your HVAC filter and looking for obvious causes of the loud noises, you’ll likely need a licensed HVAC professional to inspect and repair your air conditioner.
Frequently Asked Questions
Could a loose or damaged fan blade be causing the loud noise in my AC unit?
Yes, a loose or damaged fan blade can cause loud noises when the AC starts or stops. An HVAC technician will need to tighten or replace the affected fan blade.
Is it normal for an air conditioner to make a loud popping or banging sound when it turns on or off?
While some noise is normal during startup and shutdown, excessively loud popping or banging sounds are not typical and may indicate a problem with the compressor or other components.
Can a failing compressor lead to loud noises when the AC starts or stops running?
Yes, a failing compressor can make loud noises during startup or shutdown from the increased strain and wear on the unit. You’ll need help from an HVAC contractor to replace the compressor to fix this issue.
Should I call a professional HVAC technician if my AC unit is making loud noises when it turns on or off, or can I fix it myself?
I recommend calling a professional HVAC technician if your AC unit is making loud noises during startup or shutdown. Attempting to fix the issue yourself may lead to further damage or safety risks.
