Air Conditioner Noise Advice for Facility Managers

It’s Important to Know When to Call a Professional About AC Unit 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.





Sounds like the ones you will hear in this audio file are typical examples of what you might hear during normal operation in a healthy system.

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11 thoughts on “Air Conditioner Noise Advice for Facility Managers

  1. Outside unit comes on but no air comes from the vents, in AC mode and heat mode, it’s a goodman unit and only 4 years old….. anyone have any idea what the problem is?

    • It might be the indoor blower/air handler. You probably should not run it like that for long because it might cause further damage. Both the outdoor and indoor should be on the same control and should not be running separately but you might check to see if any breakers are tripped just in case. Also make sure your thermostat fan control is set to “on” or “auto”. If none of that works, you probably need to have a contractor look at it. My thoughts anyway. Others can weigh in here.

  2. I live in a new construction apartment building. When the ac in my unit is off, the apt is at a steady 50-ish decibels, which is standard for a quite home or street. When the ac kicks on, the noise level jumps 15 db (!!) to 65, which is the level of a normal conversation. Except, NO ONE is talking! Is this normal? I feel like I shouldn’t have to turn the tv up or down depending on whether the ac is cycling or not.


    • Hi Aaron – Hi Aaron – Sometimes the blower (fan) can be pretty loud and there can be some variability from one system to another. There are also some things in the living space that could be affecting the sound quality (tone) and/or how it travels, etc. Depending on the type of system and how close you are to it, 65 dB could be normal but you could check the spec with the manufacturer to be sure.

      You might also ask if something can be done to reduce the noise because some blower motors have multiple setting and yours might be on a higher setting than you need. The tradeoff with a lower setting might be less airflow which could lead to other problems but it might be worth asking.

      I hope this helps.

  3. There could be several possible reasons as to why a furnace High limit switch could have tripped. My recommendation would be to contact a local Trane Dealer or Distributor for their experienced advice. Another step could be to contact the OEM directly. Most OEM’s offer manuals, along with a troubleshooting guide online.

  4. I am an electrician/HVAC tech. however I am having trouble with a Trane furnace Mod.#TDX080C942C3. the flash code is 4, according to the label on the control module says this is the high temp. limit switch is open, however using an ohm meter indicates the switch is closed. I need help. could someone please call me.

    Richard Basham

  5. My central heating system is electric..I have a digital thermostat and my heater turns on and stays on for just a couple of seconds and turns off and back on again…this is repeated continuosly. what could be the problem

  6. Some help. The contractor who installed new 3 ton Goodman unit did not install TXV. Said it was a meter and didn’t need it.
    Also I heard a loud scraping noise during run. Compressor cut off during run, but fan kept running. When compressor kicked back on there was this loud scraping noise. Sounded terrible. Told contractor and he said that units make all kinds of noise sometimes, which I didn’t buy.
    It’s hard to get a good reliable contractor around here.

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