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Why Is My AC Compressor Making a Grinding Noise?

A steady hum from the outdoor air conditioning unit is all you should hear as your cooling system runs this summer. If you happen to hear a grinding noise coming from your AC compressor, this sound indicates malfunctions that need to be repaired. Star Heating & Cooling explains the possible issues causing your AC compressor to make grinding noises and what you need to do if you hear this sound from your system.

Causes of an Air Conditioner Making Grinding Noises

The compressor is located within the outdoor condensing unit of your air conditioning system. When you hear unusual noises from your home’s HVAC equipment, be sure to listen and see if the sound is coming from components inside or outside of the house. If you hear grinding noises coming from the outdoor unit, these malfunctions may be why:

1. Bad Compressor Pistons

One of the most common causes of an AC compressor grinding noise is worn-out pistons in the compressor. The compressor’s pistons function to compress refrigerant gas before it is sent to the condenser coils to release heat. As the compressor wears out, the pistons start to produce a grinding noise when your air conditioner runs. 

If your compressor is causing this grinding noise, the entire compressor will need to be replaced. Compressor replacement is typically one of the most expensive air conditioner repairs, costing between $1,800 and $2,800 on average, without warranty coverage. If your air conditioner does need a new compressor, you should consider if making this repair makes the most financial sense. In certain situations, such as with an older air conditioning unit, it may be preferable to skip compressor replacement and have a whole new air conditioner installed.

2. Worn Motor Bearings

The outdoor condensing unit contains a condenser fan and motor which run to cool refrigerant within the condenser coil. Bearings inside the motor can suffer damage from wear over time, and the motor will make a grinding noise as it runs due to the metal bearings rubbing against the metal motor housing. While this isn’t a true AC compressor grinding noise as the noise doesn’t originate from the compressor, bad condenser fan motor bearings can easily be mistaken for an AC compressor grinding noise as both components are housed in the outdoor unit. It can be difficult for homeowners to differentiate between the two issues by sound alone.

 If the bearings in your condenser fan motor produce a grinding noise, schedule an air conditioning repair appointment to correct this issue. If your air conditioner has not received a maintenance tune up recently, the bearings may just need to be oiled to eliminate the noise. If the bearings inside the motor are worn down, it may be possible to replace the bearings only, but this is often a sign that the entire motor is wearing out and should be replaced.

3. Broken Condenser Fan Blade

It’s possible for a grinding noise to occur in your outdoor air conditioning unit if the condenser fan has a damaged or broken blade. When the fan blades are not perfectly aligned, these metal pieces can hit or grind against other metal components inside the condenser unit as the fan turns.  In addition to a grinding or banging sound, this issue can cause severe damage to other system components. Because the condenser fan is located in the same unit, this sound is easy to mistake for an AC compressor grinding sound. 

You may be able to see a broken or damaged condenser fan blade by looking into the unit’s interior through the upper grille. While this isn’t a problem for DIY repairs, taking a look inside can tell you what the problem is and whether you’ll need to call for professional air conditioning repairs. 

Air Conditioning Repairs in Central Indiana

Anytime you hear an AC compressor grinding noise or grinding sounds coming from your outside air conditioning unit, shut off the system and call for professional repairs. Continuing to use the unit before repairs are made can result in more damage. Call Star Heating & Cooling today to schedule air conditioning repair services.