Phoenix Heating & Cooling Experts
Listen Up: Here’s Why Your HVAC System is Making Strange Noises

Listen Up: Here’s Why Your HVAC System is Making Strange Noises

Heating, ventilation and air conditioning systems often make weird noises. Some are normal sounds that are part of the system ramping up, blowing air or shutting down.

Most homeowners are accustomed to these sounds and don’t think anything about them. However, if your HVAC system starts sounding as if it’s crunching rocks in a cement mixer, take note. Strange noises, such as whining, shrieking, thumping or hissing, should be investigated.

Whining, Shrieking and Squealing

There are many reasons why an HVAC system may make these sounds, including a loose or failing belt, bad bearings or lack of lubrication in fan or blower motors.

If a belt breaks, the blower will not be able to turn. Operating a unit with bad bearings can cause other components to fail and waiting to make repairs can cost more in the long run. Besides, you risk not having heating or cooling when you need it if the unit breaks down.

Although some units squeal as they start up, continuous squealing should be investigated.

Shrieking coming from the outdoor unit usually means that the pressure in the compressor is not correct. If unusual sounds are coming from the outdoor unit, shut the system off and call for repairs immediately.


Hissing often indicates leaking refrigerant. Running your central air system with improperly charged refrigerant is like trying to drive with a flat tire.

A leaking valve in the compressor can also make a hissing sound. The valve controls the compression of refrigerant, which affects the pressure in the compressor. Again, efficiency is reduced, and the unit must work harder to heat and cool.

Hissing may also indicate leaking ducts. Leaking ducts can allow up to 30% of conditioned air to escape, which lowers energy efficiency, increases utility bills and compromises comfort. A certified HVAC contractor can examine ducts to see if there are holes or loose joints.

Bottom line: If you get to know the normal sounds that your air conditioner makes, you will be attuned to unusual noises that can damage your system. To reduce the likelihood of needing expensive repairs or experiencing complete system failure, have regular tune-ups to make sure all components are calibrated and operating properly. If unusual noises occur, call the experts at Custom Cooling at (602) 428-9007.


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