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What Does HVAC Banging Noise Mean?

November 3, 2021

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Never ignore an HVAC banging noise! A residential or commercial HVAC system and attached ductwork should never create banging, grinding, squealing, or other such sounds, and these always indicate needed repairs.

An HVAC banging noise can indicate a broken part or foreign object inside the AC compressor or furnace, or a compressor that is shutting down and struggling to work. Grinding noises often indicate broken parts while squealing typically means an appliance needs new bearings.

It’s always recommended that a homeowner or commercial property owner call a professional HVAC contractor for any needed AC and furnace repairs. Attempting DIY repairs or calling an inexperienced contractor can mean overlooking needed fixes, or even making the damage worse.

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A professional HVAC contractor will also be more experienced in diagnosing needed repairs and in offering quality fixes! In the meantime, however, you might note some commonly asked questions about HVAC banging noises and other such issues, so you know what to expect by way of repair work.

What Does HVAC Banging and Other Noises Mean?

Check out a few reasons why your HVAC is banging or making other noises, and when it’s time to call a professional for needed repairs. As always, ensure you’ve shut off circuit breakers before attempting DIY repairs or diagnostics, to ensure your safety.

  •  HVAC banging noises often indicate a broken part inside the air conditioner compressor or the furnace. For example, an AC piston helps control the flow of refrigerant through the compressor. If the piston breaks, it can then bang around as refrigerant moves through the appliance.
  • Loose fan blades can also bang around as the fan operates. A lost screw or another connector can also create banding sounds from inside the appliance as it runs.
  • Foreign objects inside the HVAC unit can also bang around as it operates. Small pests might crawl inside an outdoor compressor or debris can work its way from the structure’s ductwork back to the furnace or AC.
  • Bearings allow objects to spin. When the bearings wear down or lose lubrication, they often produce a high-pitched squealing sound, indicating needed replacement.
  • Belts inside an HVAC system connect gears to moving parts. Once these belts wear down or become thin, they can also start squealing.
  • Broken parts can also get stuck inside an HVAC appliance, producing a grinding sound. As motors or fans begin to break down, they might also start to grind, as they’re being forced to operate.
  • Buzzing sounds from an air conditioner might indicate that the unit is freezing up. This can be the result of overuse or of a refrigerant leak.

Why Does My Ductwork Make Banging Noises?

There are a few reasons why ductwork might make banging noises. One is the ductwork expanding and contracting as it absorbs humidity or heat and then dries out. This process can cause duct pieces to bang against the walls or each other.

Property owners should also remember that ductwork pulls air from interior spaces and passes that air through the HVAC system. Differences in air pressure between the supply and return ducts can cause an HVAC banging noise between those pieces.

Ductwork should also be secured to the area behind interior walls. If connectors or brackets come loose, the ducts can then bang as air passes through. Those connectors can also bang against wall studs or the ducts themselves.

How Do You Fix Banging Ducts?

One quick potential fix for banging ducts is to change the furnace filter. As the filter clogs, this can interfere with airflow through the ducts, causing them to expand and contract or bang against each other. A clean filter also means cleaner air throughout the home, so there’s no reason you shouldn’t give this solution a try!

HVAC banging noise in ducts

Dampers inside ductwork help control airflow and an HVAC contractor can adjust those dampers as needed. Adjusting dampers can reduce or increase airflow; in turn, this can equalize the pressure between the supply and return ducts, reducing the risk of an HVAC banging noise.

Cleaning and sealing ducts can also reduce expansion and contraction. Sealing ductwork also reduces leaking, which can lower your utility costs throughout the year. A contractor can also repair or replace damaged connectors and brackets around HVAC ductwork as needed.

Why Is My HVAC Clicking?

Repeated HVAC clicking usually has a few causes, including:

  • Thermostats communicate with the HVAC appliances through what is called a relay. This relay works as a switch; if the relay starts to break down, it might create a clicking sound as the HVAC system shuts on or off.
  • Electrical problems including bad wiring can also cause the relay to create a clicking sound.
  • The thermostat and AC compressor communicate with what is called a contactor. When the contactor is damaged, this can cause a clicking sound as the AC tries to switch on.

It’s never recommended that a property owner attempt DIY repairs for relays or contactors, as improper electrical fixes can lead to shorts and other damage.

Why Does My Furnace Clunk When It Shuts Off?

Contracting metal usually creates a clunking or HVAC banging noise as the furnace cycles off. As warm air pushes through those metal ducts, the walls soften and expand outward. Once the warm air stops flowing and the metal cools, it contracts, creating a banging, clunking, or even popping sound.

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In many cases, a dirty air filter might contribute to this issue. A clogged filter allows air to back up into the furnace system, making ducts overly warm. Changing the filter can often address this problem and reduce any clunking or other such sounds when the furnace shuts off.

If this doesn’t address the issue, schedule ductwork cleaning. Excessive dust and other debris in the ducts can also cause air to back up into the furnace area, so the ducts get overly warm. Clean ducts are also healthier for a structure’s occupants and reduce wear and tear on the HVAC system!

How Do I Reduce the Noise In My HVAC?

The first step in reducing noise from the HVAC system is to keep it maintained properly. Oiling the bearings, replacing worn belts, cleaning the units inside and out, and other such tasks will reduce the risk of damaged parts and resultant noise. Changing the filter and keeping the ducts clean also reduces pressure in the ducts and keeps them quiet!

An air conditioning sound blanket can also absorb some noise from the compressor. These blankets cover the unit and help block noise from reaching the ductwork, and can also reduce vibrations that cause noise.

A contractor can also apply sound-blocking foam to your property’s ductwork. This foam also blocks noise and vibration, keeping sound to a minimum and preventing it from traveling from room to room.

Can An AC Explode?

Air conditioners are not typically at risk of exploding! However, severe damage including worn or frayed wiring or overheating can mean a risk of the appliance catching fire.

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If an air conditioner catches fire, this can sometimes cause an explosion of the pressurized coolant. The air conditioner might also explode if it’s exposed to a fire or gases that could create the risk of an explosion.

Why Does My HVAC System Smell Bad?

Along with odd noises, it’s never recommended that a property owner overlook odd smells from their HVAC system! Note a few reasons why your HVAC system might produce odd or unpleasant odors and when to call a repair contractor.

  • An air conditioner has a drainage hose, to remove condensation from the compressor. If that hose gets blocked, trapped moisture can lead to mold and a resultant musty smell. Unblocking and cleaning that hose or tube can help prevent that issue.
  • Dead animals or insects inside the air conditioning compressor or a property’s ductwork can mean unpleasant odors. If you find a dead animal inside any part of your HVAC system, have a professional remove it and clean the area.
  • A burning smell might indicate frayed wiring or a motor leak, or a motor or blower struggling to work. Don’t use the AC if you notice this smell but leave it off and call a contractor, to prevent added damage and the risk of an electrical fire!
  • Smoky smells might be the result of cigarette smoke or smoke from cooking getting trapped in the ductwork and then becoming noticeable when the HVAC system cycles on. To prevent this issue, open windows and use exhaust fans as much as possible when smoking or cooking, and schedule ductwork cleaning regularly.
  • If you notice sewer-like smells from your property’s ductwork, the issue might be a leak from a sewer pipe or line near the air conditioner compressor. Those odors can make their way into your home from the compressor and then travel through the ductwork.

Does My HVAC System Need Repairs?

A property owner should never wait until an HVAC system shuts down completely before calling for repairs! Your air conditioner or furnace might still operate even when damaged, but the longer you put off needed fixes, the more costly your eventual repair bills. Check out some indications that it’s time to schedule HVAC repair or replacement.

  • If your air conditioner doesn’t keep interior spaces at comfortable humidity, it typically needs repair or replacement. An air conditioner should remove excess humidity from the space, not just heat, so call an HVAC repair person if interior rooms feel cool but “clammy.”
  • Weak airflow also indicates damage and the need for repairs or HVAC replacement. A slowing motor or damaged blower can allow for some airflow but the longer you ignore this issue, the more likely that the system will simply shut down.
  • Ice forming around an air conditioner compressor can indicate that condensation is not draining properly. This condensation can back up into the appliance and cause permanent damage.
  • Your HVAC system should cycle on and off automatically, and shouldn’t run too long or shut off too quickly. If the HVAC system doesn’t cycle on or off as it should, this can indicate worn wiring, a bad relay or contactor, a damaged thermostat, or other such needed repairs.
  • Air conditioning coolant doesn’t evaporate or otherwise needs replacing. However, a lack of proper cooling can result from a leak in the compressor hose. A contractor can fix that leak and recharge the coolant as needed.

Should I Repair or Replace an HVAC System?

Replacing an HVAC system is not always an easy decision, as an entirely new air conditioner, furnace, and air filter can be costly! However, it can sometimes be more expensive to repair an older system than to invest in new HVAC appliances. How so?

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First, note that an older HVAC system will probably need several repairs as it reaches the end of its expected lifespan. In turn, you might wind up spending hundreds if not thousands of dollars on repairs for a system you’ll need to replace eventually! Investing in new HVAC now can mean avoiding those repair costs while enjoying a high-quality heating and cooling system.

Energy-efficient air conditioners and furnaces might also mean reduced utility costs over the years. An older HVAC system not only wastes energy but it also might not function as expected, so you’re paying more money in utility costs for less heating and cooling!

Outdated HVAC systems can sometimes affect property values, making your home or commercial structure less desirable to potential buyers. Even if you don’t plan on putting the property on the market, lower property values can mean less equity and less chance of qualifying for equity loans. Investing in a new HVAC system can protect or even increase your property values while potentially saving you money over the years!

Cypress AC Repair Pros is happy to bring this information about what an HVAC banging noise means to our readers and hopefully, it helped answer your questions! If you need high-quality, affordable AC and furnace repairs for your property, call our Cypress HVAC repair contractors today. We start every project with a full inspection and offer only the highest-quality appliances for your home or business. To find out more, just give us a call.

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