Scary Noises You Do Not Want To Hear From Your Central Air Conditioner

If you are like most people, you know the noises that your home normally makes. The hum of your outside air conditioning unit generally means that you will soon feel the cool air blow from your vents. But every now and then your unit may begin to make unusual noises you are not used to hearing. These noises generally mean that something is wrong within your unit. Knowing how to differentiate between these noises will give you an indicator of what may be wrong.


A hissing noise coming from your outside unit is not always a bad thing. If the hissing is only a few seconds long and happens at regular intervals, this is probably just a normal part of the cooling process. The hissing often originates from your expansion valve when your liquid refrigerant expands, or changes to a vapor form within the evaporator.

If the hissing noise is lasting for long periods of time, and seems to come from your compressor area when your unit is powering down, you may have a leak in one or more of your internal valves, or you may have too much internal pressure in your compressor. This excessive pressure could be caused by a blockage somewhere within your system. Both of these conditions are something that needs to be addressed by a licensed service technician immediately.


A high pitched whine, or scream may also be an indicator of high internal pressures within your unit. If these noises are heard, you should turn your unit off immediately and call for a service technician. Other reasons that your unit may scream includes:

  • Motor bearings going bad
  • Mechanical shaft bearings going bad
  • Debris clogging your system and more


Most people have heard the screeching sound of a belt going bad on their car. A bad, or worn belt, on your air conditioning unit will produce the same type of screeching or squealing noise. This type of noise is usually heard when your system first turns on and begins to cool the air down. If the noise is brief and it just happens upon startup, it may be a normal noise your compressor makes upon start up that has simply gotten worse. A worsening noise may be an indicator that your compressor is going bad.

Banging, Clanging, And Knocking

The vibrations of your air conditioning unit can cause screws, nuts, and bolts to work themselves loose over time. A loose bolt within your unit can allow your internal components to slightly shift. This may cause your fan blades to strike the fan guards, or strike each other.

Occasionally sticks, limbs, and other debris will fall down within your unit. Any type of debris can also cause your unit to make these types of noises. Turn your unit off, and peer down into your outside unit to look to see if you are able to spot anything that should not be there. If you do not see anything, and the noise continues when you turn your system back on, call for service.

Unless you have had some type of specialized training, you probably will not be able to diagnose and fix your central air conditioning yourself based on the sounds that it is making. Being able to describe the sounds you are hearing will give your service technician clues as to where to start their inspection.  If your unit is still under warranty and you attempt to fix it yourself, you may actually void your warranty, and you do not want to do that. Because depending on the type of warranty you have, the service visit may even be covered.

If you're having conditioning troubles, contact a local professional, such as HomeSmart From Xcel Energy, for more information. 

About Me

Keeping Your Appliances Running Well

A few years ago, I decided to install a dishwasher on my own. Unfortunately, after only a few days, it started leaking badly and I realized that I needed to have it professionally repaired. Appliance problems can happen in a jiffy, which is why it is so important to look after your devices. After that experience, I learned how important it was to have appliances installed by an expert and to care for them so that problems didn't pop up in the first place. This blog is all about keeping your appliances in tip-top shape by looking after them on a daily basis.