Why Is My Central AC Making Loud Noises? A Twin Cities Tech Answers

Tired of hearing strange, loud noises coming from your AC system? We don’t blame you. They’re obnoxious and you probably wonder if it’s cause for concern.

It’s normal for an AC system to make some noise when it kicks on and to hum quietly during operation. But, if you’ve never heard these sounds before, your system might be dealing with a more serious problem that needs addressing before it impedes operation or performance.

In order for a professional technician to diagnose the issue and repair your AC, they will first categorize the sound to find the source. The 4 types of noises that could require an AC repair include:

Hear any of these noises? If so, you should immediately schedule a repair with a professional HVAC technician. During the diagnostic, make sure to describe the sound.

Any banging noises coming from your AC could be caused by something as minor as a loose screw or as major as the fan belt attached to the motor breaking apart.

Loose AC parts slamming against other parts will produce a banging noise. They vibrate on the unit’s floor or against its walls when they break off. For example, when the mount stabilizing the AC’s blower wheel breaks, the fan it holds up falls and slams against the unit's casing.

Another reason for banging noises is a broken AC compressor or an incorrectly-mounted one. If your AC system starts shaking while running, you can tell this is the issue.

Due to normal wear and tear, parts within the compressor get loose and rattle around inside its outer casing. This is problematic because the compressor is the “heart” of the entire system and is difficult for technicians to repair, as it’s hermetically sealed. In most cases, you will need to replace your AC system entirely.

Learn more in our article, “How Much Does It Cost to Replace an AC Compressor?”

If you only hear banging noises when you’re near your AC’s outdoor unit, the following causes could explain them:

• Leaves and twigs getting lodged inside it
• Screws holding together the outdoor unit’s panels falling out
• Springs mounting the refrigerant pump breaking

Solution: Contact an AC technician to repair, replace, and clean worn-out and loose parts to prevent more parts from breaking down.

Hearing buzzing noises near your AC’s air handler or the outdoor unit? Or is the AC clicking more than once when you try to turn it on, but it won’t start? These noises could be caused by:

• Faulty thermostat parts
• Loose or exposed wiring (you should see sparks and electrical discharge)
• Improperly connected electrical wires to the AC’s circuit breaker
• Faulty electrical signals in the control panel (you see electrical sparks)
• A broken condenser fan
• A broken capacitor or contactor (both are vital in helping the system start)

Small objects nesting inside the AC's blower can also cause clicking noises. If you hear the sound when the AC is running, the object is hitting against the fan as it spins.

Solution: Any of these problems could indicate deeper electrical problems. Keep your system turned off and immediately call a professional HVAC technician to diagnose and resolve the issue.

Hissing noises could be a sign of the following AC problems:

• An improperly sized filter
• A refrigerant leak

Most likely, the problem is a refrigerant leak. Refrigerant is a cold chemical agent that plays a vital role in cooling your home. It normally circulates between your AC system’s indoor and outdoor units in a loop as it absorbs heat to dump outside.

Over time, the refrigerant lines and coils that transport the refrigerant wear out, forming leaks. A hissing sound then occurs when the air and refrigerant touch.

How do you know if you have a refrigerant leak?

• Your AC vents blow warm air even when the system runs
• Your energy bills have increased despite usage staying the same
• Your AC takes longer to cool your home
• Your AC cycles on more frequently

Learn more in our article, “How to Tell If Your AC Needs More Refrigerant.”

Solution: If you suspect a refrigerant leak, contact a professional AC technician right away to inspect the refrigerant lines and coils and recharge the agent.

The cause of any loud screeching or squealing noises coming from your AC depends on which unit you hear it from.

If you hear the noises coming from the outdoor unit when it’s running, a bad compressor motor or a faulty outdoor fan motor is the culprit.

If the noise comes from the inside unit, a faulty blower fan motor is the cause. This blower fan pulls in warm air from your home to be cooled and then pushes the now-cooled air throughout your home. Screeching occurs when the bearings in the fan motor break.

Solution: These parts are all critical for an air conditioner to function. Contact a technician ASAP to repair or replace your AC system’s compressor, outdoor fan motor, or blower fan motor.