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Douglas Cooling & Heating Blog

Common AC Noises and What They Mean

By this point in the year, Birmingham area residents are already used to the steady hum of the air conditioner running. This is one reason it comes as a surprise when the cooling system starts singing a different tune! Some common AC noises are undeniable and are typically the ones that spell trouble.

If your air conditioner is making sounds other than the typical humming, don’t fret – our team explains what air conditioning noises usually mean and what we do to correct them.

Clicking Noises

You may be used to hearing a slight click as a cooling cycle starts then again as it ends – that’s normal. What is not normal is clicking that occurs throughout the cooling cycle. If the noise comes from the indoor air handler or outdoor condenser unit, this kind of clicking is typically a sign that a control within the cooling system has malfunctioned. If you hear clicking from around the thermostat, the thermostat may be the system control that has gone bad.

These air conditioning noises typically warrant replacement of the offending component. A technician inspects controls in the component where the noise originates to find the source of the sound. If your thermostat has gone bad, we can install a new one quickly.

Banging Sounds

A banging sound coming from your outdoor cooling equipment as it operates is a sign something has come loose related to the compressor. A bolt holding down the unit may have come loose, which needs to be re-tightened. Or, a piston pin, rod or other interior component may have come loose inside the compressor. In this case, compressor replacement is often recommended as an attempt to repair the issue may not be worthwhile due to the way this component is constructed.


A squealing noise from the indoor air handler unit is typically made by the blower motor belt when it needs to be replaced. The repair is fairly straightforward – a new belt needs to be installed. However, do not wait to have this fix completed because if the belt does break, you won’t be able to run the cooling system until a new belt is in place.

Squealing from the outdoor unit is another issue entirely. A very high-pitched squeal, or a noise that sounds like a scream, is often indicative of high pressure within the system’s compressor. If you hear this concerning noise, shut the cooling system off immediately. Sometimes, the squealing noise is accompanied by a hissing sound.

When pressure rises in the compressor, a sensor typically shuts down the system for safety. The sensor may be faulty and require replacement. A valve within the compressor may have been damaged, causing the high pressure levels. 


If a hissing noise is heard with squealing or screaming, high pressure in the compressor is typically the issue. Hissing can also indicate a different issue – a refrigerant leak. You may notice hissing anywhere along the refrigerant line and connected indoor and outdoor units. 

To repair this issue, a technician first finds the location of the leak. Repairs are made, and the system’s refrigerant charge is measured. If the system leaked enough refrigerant, refrigerant levels must be recharged to ensure the air conditioning system has appropriate refrigerant to cool the home.

Call Douglas Cooling & Heating When You Notice Air Conditioner Noises

These air conditioner noises don’t happen too often to Birmingham homeowners, but when they do, air conditioner repairs are needed to avoid damage to system components and an interruption in equipment service. If you hear any of these air conditioning noises this summer, call Douglas Cooling & Heating for reliable repairs to your cooling system.

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