Why Does My Air Conditioner Make a Loud Noise When It Turns Off?

When it’s unbearably hot and humid outside, a malfunctioning air conditioner can prevent you from staying cool and comfortable inside.

One common and distracting issue during the summer is an air conditioner that makes a loud noise when it turns off. HVAC.com explains common causes of this and preventive measures to help keep your system running properly – and quietly! – all summer long.

What Is the Normal Sound an Air Conditioner Makes When It Turns Off?

If you hear a few brief, soft sounds as the air conditioner turns off, don’t worry – that’s normal. These noises can include a gentle whooshing sound as the air stops flowing, a faint click as the thermostat switches off, or a low hum as the fan gradually winds down. You might also hear a slight popping or ticking noise from the ductwork as it cools and contracts. 

These sounds should be brief and minimal and indicate your air conditioner is working properly. If the noises are more jarring, it could be a sign that something is wrong.

Common Reasons Why Your AC Makes a Loud Noise When It Turns Off

Several issues can cause loud noises when your air conditioner shuts down, including:

1. Compressor Issues

The heart of your air conditioning system, the compressor is responsible for circulating refrigerant and maintaining pressure. If you hear a loud banging or clanking noise, it might be due to a loose or damaged compressor. This can be a serious issue, as the compressor is an expensive component to replace.

2. Loose or Damaged Parts

Air conditioners have several moving parts, and over time, these can become loose or worn out. A rattling or banging noise when the air conditioner turns off could indicate that a component, such as a fan blade or motor mount, is loose or damaged. 

3. Faulty Motor Bearings

The motor in your air conditioner relies on bearings to reduce friction and ensure smooth operation. Over time, these bearings can wear out, leading to grinding or squealing noises. If you suspect this is the reason your AC makes loud noise when it turns off, contact a professional to help avoid further damage to the motor.

4. Electrical Problems

Faulty capacitors or loose wiring can cause clicking or buzzing noises when the AC powers down, leading to potential risks of electrical shock or fire. Reach out to a qualified technician immediately if you suspect an electrical issue.

Diagnosing the Noise: When to Call a Professional

If your AC is making a loud noise when it turns off, turn it off. Running an air conditioner with issues can cause increased damage, which may lead to a more expensive repair or even a total system failure.

Next, do a quick inspection. Check for any loose panels on the indoor unit or debris around the outdoor unit that might be causing the noise. Ensure the air filter is clean and replace it if necessary. If the noise persists when you restart the system or you notice any signs of damage, it's important to contact a professional HVAC technician. 

Tips to Keep Your AC Quiet

Preventing loud noises when your air conditioner turns off involves regular maintenance and a few proactive steps:

Regular Maintenance

Schedule AC maintenance with a professional HVAC technician once a year. During these visits, the technician will inspect, clean, and tune up your system, addressing potential noise issues before they become major problems.

Keep the Area Around the Unit Clean

A simple tip you can do on your own is ensuring the area around your outdoor unit is free of debris, vegetation, and obstructions. This helps maintain airflow and prevents damage to the unit.

Insulate Ductwork

Properly insulated ductwork can reduce noise caused by expansion and contraction. Insulation also improves the overall efficiency of your HVAC system.