Is That Normal? Sound Advice About Air Conditioner Noise

Sometimes our cars, appliances, and even air conditioners make the strangest noises, but how do you know if they’re normal or if something might be wrong? It’s not always as easy as hitting the ‘restart’ button on your computer, so it’s important to know when you should call a professional or contractor to check it out. The following are some tips about what sounds are normal and what indicates professional problem when it comes to your air conditioning unit.

Outdoor unit noise is normal upon start-up and shut down. The outdoor unit is where most of the mechanical operations in your system take place and depending on the type of equipment, it can be noisy and somewhat varied when it starts up and/or shuts down. Typically, most air conditioners make noise when they first cycle on, which can be caused by the buildup of pressure in the refrigerant lines or from bearings, fans or other moving pieces starting up. The same is true when the unit cycles off, or comes to a stop, as the pressures need to equalize. Sometimes this causes a unique noise that sounds like air escaping, a click or rattle.
◾Tip: If the start-up and shut down sounds are the same from cycle to cycle and not too loud, it’s probably normal and not worth calling a contractor.

Outdoor unit running noise after start-up can also vary among different types of equipment. Once the outdoor unit starts up, it should reach a consistent sound where you hear the fan blowing and the other mechanical parts humming along. Sometimes you might hear a cycling sound over the period of a few seconds where the unit changes the pitch of its normal running sound and might get louder or quieter in “waves.” If it gets increasingly louder as the system is running, then it might require a contractor to see whether it is out of balance or requires further inspection. If you hear a loud, intermittent mechanical “scraping” or “banging” noise, this is not normal and you should shut your system down and call a contractor to inspect it as soon as possible.
◾Tip: Significant changes in pitch or ‘banging’ noises indicate you should call a contractor.

Indoor unit sound is usually the sound of the fan moving air through your system. It is most noticeable when the system turns on and off. If you have a high efficiency system (16 SEER and over) you could hear two distinct sounds as your system moves from high to low cooling speed. The high speed sound can be noticeable, but the low might be so quiet you can barely hear it.
◾Tip: Air moving through your system should sound smooth and consistent once it is running.

In general, sound is a subjective attribute and the above descriptions are provided as a guideline for noises that could potentially signal a costly problem. In addition, we have recorded some typical compressor sounds you might hear during a normal start up, run and shut down cycle as examples

Our goal is to help educate our customers about energy and home comfort issues (specific to HVAC systems). For more information about Indoor Air Quality and other HVAC topics, click here to visit our website.