Why Air Conditioner Makes Loud Slamming Noise When Turning Off

A loud slamming noise coming from your air conditioner every time it shuts off can be discomforting. Well, this is a reality for some homeowners, and it happens because of various reasons that we are going to tell you shortly. Depending the cause, the solution can range from a simple DIY or to hiring a professional AC tech.

If you are having such a problem with your AC, the first thing you need to do is to establish exactly where the noise is coming from. If it is coming from inside your home, it could be because of following reasons:

Air filter is slamming against the frame, sheet metal or the grille

Air filters help remove dust and other contaminants, helping to maintain good indoor quality in your home. They also protect the indoor AC coil from excessive dust and debris that will reduce energy efficiency and, possibly lead to early mechanical failure.

If the air filter is loose, it can move back and forth under the power of the blower motor when it’s turned on. The filter is sucked up to the top of its metal enclosure when the AC first turns on. After the AC stops pulling in air and shuts off, the filter drops onto the return grille, making the loud slamming noise.

Solution

Remove the filter, and run your AC for a cycle or two. Do you still hear the noise? If it stops it’s an indication the filter is the problem. Check if the filter is dirty. Rather than allowing air through it, a dirty filter moves entirely, making the noise. Try cleaning the filter or replace it, and put it back.

If the filter is clean but the problem is still there, inspect the return grille to see if the air filter is fitted properly. You can use a tape to hold it place if it’s not secured. The filter also needs to be the correct size for your system. Try using a filter with a lower MERV rating.

Check this too: Honeywell Home T9 Smart Thermostat Troubleshooting and FAQs

If the problem isn’t with the air filter itself, it could also be that your return ducts are undersized. Air can travel faster than normal when the ducts are undersized, causing the filter to get sucked up then drop when the air stops flowing. You may need to call a technician to determine if this is the problem and modify the ductwork to stop the air filter from getting sucked up.

Loose blower fan

Blower fan mounts can become loose over time and the fan may be out of balance. This causes the blower wheel to bang against its metal casing when the fan slows down with the shutting off the AC.

Solution

Try tightening the bolts that hold the blower motor in place. If this doesn’t solve the problem, call an HVAC technician to diagnose the issue, and recommend the best solution.

Expanding and contracting ductwork

If you have sheet metal ducts, they can make some noise when expanding and contracting from pressure/temperature changes. This doesn’t necessarily mean something is wrong with your air conditioner.

Solution

If the sounds are loud and more frequent, you may want to call a technician to inspect and make sure the ducts are properly sized and reinforced. The technician can add ductwork insulation that can help reduce the noise.

Closing damper

Some homes have dampers installed in the ductwork to direct air to certain rooms. When the damper is closing, it can make slamming noise.

Solution

While this also doesn’t mean something is wrong with your AC, you may want to have a technician inspect the damper and make sure it is properly installed if you find the noise too distracting.

If the slamming noise is coming from the outdoor part of your AC, it could be one of the following issues:

Broken compressor springs

The compressor, located in the outdoor unit, circulates refrigerant in your AC system. It is the hermetically-sealed cylinder. Inside the compressor, casing in pumps that are normally supported by springs. If the springs get worn out or break over time, the loose pump can bang against the compressor casing, causing the slamming sound you might be hearing.

Solution

You may want to get an HVAC technician to check and tell you the repair options you have. Fixing these springs is not easy and you may have to replace the compressor.

Broken outdoor fan

The outdoor fan helps disperse heat absorbed by your AC system. It can become loose from wear and tear, consequently hitting the metal parts in the outdoor unit when slowing down after shutting off the AC. You will likely be able to determine if this is the problem if standing next to the outdoor unit when a cycle starts and stops.

Solution

Contact an AC repair technician to diagnose the problem and recommend the best solution. The technician will inspect the outdoor assembly and make sure it is tightly secured and running properly.

Check this too: Shark Ion Robot Troubleshooting Guide