My Outdoor Unit (Condenser) is Making A Weird Noise

Condenser beside house

The outdoor unit for your HVAC system is the condensing unit. To learn more about what the condenser does read our post here. For straight AC systems the condenser only runs in cooling mode. For heat pump systems the condenser runs in heat mode as well. 

The condenser is a fairly simple mechanical unit and only has a few components that can make noise. Depending on the type of noise we can then determine which component is failing or otherwise not operating as designed. 

Here are a few types of noises you may hear:

  1. Electrical buzzing
  2. Knocking or grinding 
  3. Mid to high pitch humming
  4. Loose rattling
  5. Overall rattle (like an off-balance dryer in your laundry room)

Electrical Buzzing

Inside the control panel of your condensing unit is the contactor. When the thermostat engages the condenser it does so by using low voltage to close the contactor. Once the contactor closes high voltage now passes through it to the other components inside the condenser. 

High voltage comes into the bottom of the contactor directly from the high voltage disconnect on your home. The contactor is basically a switch, like the light switch on your wall. When the contactor closes, or engages, the high voltage can now pass through it. 

When contactors begin to fail they rattle and buzz from the voltage passing through them. They can fail from corrosion and build up on the contacts, weathering, bugs getting in to them, or parts getting loose and failing. 

The way we fix this is to either clean the contactor of the debris causing the noise, or if it is corroded too badly or has parts failing we simply replace it. It is a quick fix and easy to resolve. 

Knocking or Grinding

Inside the center of the condensing unit is the compressor. It takes a low pressure refrigerant in gas form and compresses into a high pressure and high temperature gas that can then be condensed into a liquid. If you get low on refrigerant or the compressor begins to fail it gets loud and begins to knock or grind. 

Unfortunately, compressors are hermetically sealed components, which means we can’t open them up and repair them. If the compressor is failing it has to be replaced. When this situation comes up (which is rare) we usually recommend replacing the entire outdoor unit. The cost to replace a compressor is almost as much as replacing the entire condenser and a compressor only comes with a 1-year warranty from the manufacturer. A new condenser comes with a 10-year warranty. Because of these factors we recommend replacing the entire outdoor unit. 

Mid to High Pitch Humming

On the top of your condenser is the fan and motor. The fan pulls air through the condenser, over the coils, extracting heat from the refrigerant to condense the high pressure gas refrigerant into a liquid. If the fan motor begins to fail, or if the fan blade is damaged or off-balance in any way the fan will begin to hum. 

Condenser fan motor and fan blade

In this scenario we will inspect the fan blade for damage or balance issues and then run diagnostics on the fan motor. If we can reset the fan blade on the motor we may be able to fix the hum, otherwise we have to look at replacing the fan motor, the fan blade, or both. This usually takes an hour or so to complete but resolves the issue immediately. 

Loose Rattle

Many customers complain of a loose and annoying rattling sound coming from their outdoor unit. Typically this is just a loose screw that has given opportunity to one of the panels on the condenser to vibrate and rattle. There usually isn’t a bigger, underlying issue involved with this type of noise. 

When this happens we inspect the condenser and find the missing screw or the loose panel and either add a new screw or simply tighten the existing ones. In more extreme cases we add a bit of rubber backing under the noisy panel and then tighten the screw. This usually resolves the issue. 

Overall Rattle

Occasionally we get customers complaining of a much louder, harder rattle from their condenser. This one is closer to the sound of an off-balance washing machine or dryer walking around in your laundry room, and is due to the same cause, the condenser is off-balance. 

This can be caused by a number of different issues. If the condenser fan motor is coming loose from the shroud, or if the fan blades are off-balance, or if the condenser pad is no longer level, etc. 

In cases like this we need to find the cause of the imbalance and try to resolve the issue by re-securing the fan motor to the shroud, re-leveling the condenser pad, etc. Sometimes it will be a bad component causing the imbalance and sometimes it’s just time and outdoor weather conditions that cause the issue. 

Wrapping Up

In summary, noisy condensers are annoying, no doubt, but they provide a warning to you as the homeowner that something is going wrong, and necessary clues to us as to what needs to be repaired. 

If you experience problems with your condenser call Prestige Air. Our expert service professionals have the training and experience to keep your HVAC system in tip-top shape all year long. Call (817) 200-7215 to make sure your heating and cooling are ready for the season!

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Prestige Air proudly serves Northeast Tarrant County and the Fort Worth, Texas area including Hurst, Euless, Bedford, Colleyville, Grapevine, Southlake, Keller, Watauga, Haltom City, and North Richland Hills.

We look forward to serving you and your household!