My Air Conditioner Makes Slamming Noises When Turning Off: A Phoenix Tech Explains

Does your air conditioner make a loud slamming noise whenever it shuts off? This happens from time to time, and while it’s hard to know the exact cause without an in-home diagnostic, we can give you some general information about the potential underlying issues.

For added peace of mind, we always recommend having a professional technician take a look, especially if this is the first time you’ve heard the noise.

To help you troubleshoot the issue, let’s review some common culprits:

We’ll go review what an HVAC professional can do to resolve them.

Does it sound like there is a door inside your air ducts that slams shut whenever the AC turns off? If you hear the slamming sound coming from inside your home, you may have one of the following problems:

• Air filter slamming against the return grille
• A closing damper
• Air ducts contracting
• Blower fan problems

Most homes in the Phoenix area have return air grilles (vents) located on the ceilings of their homes. Warm air enters these grille openings. Before being cooled, the air goes through a filter first.

Sometimes, the air filter can get sucked up to the top of its metal enclosure when the air conditioner sucks in the warm indoor air. When the air conditioner turns off and stops pulling in air, the filter drops to the grille, creating slamming noises. Usually, this occurs due to:

An efficient air filter

Highly-efficient air filters are normally great for improving a home’s air quality. However, they can restrict the amount of airflow going through the filter as they get clogged with debris faster. So, when the AC tries to pull in more air, the filter gets pushed to the top of the ductwork. It’s also possible the air filter isn’t properly fitted and the right size for your system.

We recommend replacing your air filter more frequently instead of downgrading the filter’s efficiency. If you use a less efficient air filter to prevent the noises, pair the filter with an air scrubber that catches airborne contaminants without restricting airflow.

Undersized return duct:

If your return ducts are too small for your HVAC system, the speed of the air going through the ducts can be faster than normal. The powerful air currents can suck up an air filter to the duct and then drop it when the AC turns off. Contact a professional to determine whether this is your problem and if the ductwork needs modifications.

Some air conditioning systems have dampers that direct the airflow to certain rooms of your home. The slamming noises could simply be the dampers closing after the AC shuts off.

If the slamming is distracting, have a professional technician inspect the dampers to ensure they work correctly. Otherwise, this may just be business as usual.

Most homes have sheet metal ductwork, so you may hear slamming noises due to the ducts expanding and contracting from pressure and temperature changes. Some homeowners also refer to the sounds as a “popping” noise.

A certain amount of sound is normal, but if you keep hearing frequent loud sounds, have a professional inspect your ductwork. They should be adequately reinforced and sized for the amount of air going through them regularly.

You may have a problem with your indoor unit’s blower fan. It pulls in warm air to be cooled and then pushes cool air throughout your home. Over time, its mounts can loosen, causing the blower wheel to bang against its metal casing. Without proper mount support, the blower wheel becomes off-balance whenever the fan slows down during the air conditioner shutdown process. Have an HVAC professional inspect the blower wheel assembly and tighten any loose connections. The mounts may need repair or replacement.

If you stand beside your air conditioner’s outdoor unit when it shuts off, do you hear a loud bang that sounds like something hitting a wall? If you hear the slamming noises coming from outside your home, your AC most likely has one of the following issues:

• Broken compressor springs
• Loose outdoor fan

An air conditioner’s compressor is a part of the outdoor unit and plays a vital role. It pumps the chemical agent, which removes heat from your home's air, to and from the indoor AC unit. The compressor is within a hermetic seal, along with a refrigerant pump.

This refrigerant pump is mounted with support springs. Once a spring breaks, the pump can’t hold itself up anymore and knocks against the compressor’s casing, creating a slamming noise.

You’ll have to contact an HVAC professional for assistance to get rid of the noise. Compressor repairs almost always need replacements, which can be pricey as the tightly-sealed compressor is a vital AC component. Instead, most homeowners replace their entire AC systems, especially if the compressor is still under warranty.

Like the indoor AC unit, the outdoor unit also has a fan to disperse heat absorbed by your air conditioner outdoors. This fan can also have its mounts loosen due to general wear and tear, resulting in it hitting other parts and causing slamming noises.

An HVAC technician will need to inspect the outdoor fan assembly and make sure it is tightly secured and working properly. You may need a new fan assembly or a few bolts tightened.