Why is my air conditioner making a loud grinding noise?

Why is my air conditioner making a grinding noise?


The first thing you should do if your air conditioner is making a grinding noise is switch the unit to off at the thermostat. A/C units tend to get louder as they get older but a grinding sound is never normal and always an indication that something has gone wrong.


Of course, air conditioners always break down at the most inopportune time – when it’s hot, and you need it most! As I type this in July, it’s about 110 degrees at Magic Touch’s office in Mesa, AZ, so if you live nearby you’d probably be hesitant to turn off your air conditioning unit right now. Don’t, go shut off your AC unit right now and then come back to finish reading this.


Why is shutting off an AC making a grinding noise so important?

Since we know a grinding sound is never normal, we know something is wrong! An air conditioning unit is made up of a lot of different components. Very often the failure of a major component, a compressor for example, is caused by a smaller failure that went undiagnosed for a while. This is the reason regular cleaning and maintenance is important, but that’s for another post.


What components are the most likely to make a grinding noise in an AC unit?

To understand why your unit is suddenly making a grinding noise let’s cover which AC parts actually move, as a grinding sound is most likely to be caused by a part that moves (with one exception – described below).


Condenser Fan – also known as the outdoor fan motor, the condenser fan motor is located outside in the condensing unit aka outdoor unit. If you have a rooftop package unit, your condenser fan motor is the one that can be seen looking through the grill on the top of the A/C unit. There are two failures associated with the outdoor motor can make a grinding noise:

  1. The bearings inside the motor itself have gone bad. This is a very common AC failure requiring repair.
  2. The fan blade has broken and is rubbing against the motor or AC unit cabinet. This is a little less common failure than bad motor bearings, but does happen and can cause other problems if not addressed right away.

What does a condenser fan do? The condenser fan motor is used to release heat that was absorbed from inside the home and expel it outside. It also helps to keep the air conditioner’s compressor cool.


Blower Fan – also known as the indoor fan motor, the blower fan motor is located in the furnace or air handler (typically in an attic, indoor closet, garage, crawl space, or basement). If you have a rooftop package heat pump or gas-pack, the blower motor is inside the unit on your roof. There are two ways a blower fan motor can make a grinding noise:

  1. The motor bearings are bad. This is a less common failure than a condenser fan motor failure, but still a semi-common AC repair out of the thousands of AC repair calls we receive every year.
  2. Blower motors use a round “squirrel cage” fan blade as opposed to an axial fan blade like the blade a condenser motor uses. An axial fan blade is like the fan blade in a box fan you may have had in your living room as a kid. Think of a squirrel cage like a hamster wheel they look similar. When a squirrel cage blade breaks, or the bolt that holds it to the motor shaft breaks, it can rub against the fans housing and cause a grinding noise.

What does a blower fan do? The blower fan motor aka indoor or evap. Motor, is used to push the conditioned air into the air duct system. When you put your hand in front of an air register (vent), and feel the air blowing out of it, you are feeling air being moved by the blower motor.


AC Compressor – the compressor is the heart of an AC unit. The compressor is basically a pump that moves the refrigerant through the air conditioner’s pipes and facilitates the refrigerant’s conversion from a liquid to a gas over and over again. Inside the compressor are either valves that open and block an opening (like a car engine), or sometimes a component that looks similar to a drill bit that spins. While typically not described as a grinding noise when these valves fail, or are failing, they can be noisy, and some people describe it as a grinding noise. Obviously, everyone can describe a sound a little differently. Need proof? – describe the sound a violin makes! It’s a HVAC Technician’s job to interpret the sound based on experience and his or her training.

One noise sometimes described as a grinding noise that doesn’t have anything to do with a moving part is the sound a reversing valve makes when shifting from heating to cooling. Technically a moving part is involved but it happens only one time for a brief moment and then stops moving. This sound is actually a normal sound on a heat pump and only happens when the unit starts or stops. If the sound is constant, it is not coming from your heat pump’s  reversing valve.


How do you fix an air conditioner making a grinding noise?

I write these blog posts for consumers so they can make an educated decision about home repairs, energy efficiency, HVAC, etc. when working with licensed, qualified, professionals. I do not recommend anyone without formal HVAC training and experience attempt to fix these items themselves. In the twenty-years I’ve run an AC Company in Mesa, AZ, and the ten-years prior to that working as an HVAC installer and technician; I’ve seen a lot of “handy” homeowners do more harm than good – even some that would’ve been a minor repair for a contractor that required replacing entire heating and cooling systems after someone’s, friend’s, cousin Larry was done with it.

Obviously, I recommend calling a local air conditioning repair company if your ac unit is making a grinding sound. However, now you understand what these components are and what they do so you will be better prepared to speak with your AC technician.


How much does it cost to fix an A/C making a grinding noise?

There are too many variables to answer a question this broad precisely, however to give you a general idea here are a few average ranges:

Replacing a condenser fan motor can range from a few hundred dollars to many hundreds of dollars on high-end variable speed motors.

A new blower motor can run from only a few hundred dollars installed for some “universal fit” motors to over a thousand dollars for OEM (Original Equipment [from] Manufacturer) and variable speed motors.

A compressor replacement can sometimes be a large enough ticket item to consider replacing the entire AC System, but in general can range from $1,500 to as high as $3,000 and average over $2000 in most cases.


Magic Touch Mechanical is an award-winning air conditioning company serving Phoenix, AZ and nearby cities for over 20-years. If you need AC repairs, replacement, or installation, contact us today!