A hissing air conditioner or other unusual noises may indicate that your HVAC system is experiencing pressure-related issues that could make it unsafe to continue running. If your AC is producing strange sounds, it's highly recommended to turn off the system immediately and call a professional to assess the situation.
When your air conditioner emits a hissing noise, it could be due to one of the following issues:
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Refrigerant leaks
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High pressure in the compressor
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Leaking air ducts
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Faulty reversing valve (for heat pumps only)
We will explore each of these potential problems in detail and explain the necessary steps to resolve them. Additionally, we will guide you on how to identify early warning signs of AC trouble, so you can prevent unexpected breakdowns during critical times, such as the peak of a hot Georgia summer.
If you need a professional to diagnose why your AC is hissing, contact Reliable Heating & Air at (770) 594-9969 or schedule an appointment.
With over 200 trucks and 300 technicians, we guarantee fast service to diagnose the hissing noise and promptly repair your air conditioner.
Cause #1: Why is My AC Making a Hissing Noise? Common Issue: Refrigerant Leaks
Refrigerant leaks are the most frequent cause of a hissing air conditioner. When your AC has a refrigerant leak, you may hear a hissing or bubbling noise coming from the compressor located in the outdoor unit. Since the system is pressurized, the hissing sound occurs when pressure is lost due to a refrigerant leak, especially if the leak is significant.
If your AC is making a hissing noise and you also notice any of the following signs, it's likely caused by a refrigerant leak:
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Ice on your AC
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Vents blowing warm air
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Energy bills that are higher than normal
Cause #2: AC Making a Hissing Noise When Turned On? It Could Be High Compressor Pressure
The compressor is a critical component of your AC that circulates refrigerant throughout the system. Since it is pressurized, it can emit a hissing or screeching noise if there is excessive pressure. This is most likely the cause if the sound begins when the AC starts and lasts for around 10-15 seconds.
Signs that high pressure in the compressor may be causing the hissing noise include:
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The screeching or hissing sound starts when the AC kicks on and lasts for 10-15 seconds.
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Your system starts and stops more frequently than usual.
Cause #3: Hissing Sound from AC Ducts? Leaking Air Ducts Might Be the Cause
Over time, the air ducts of your AC system can degrade and develop gaps, cracks, or tears through which air escapes. Many homeowners report hearing a hissing or high-pitched whistling sound from their vents, which is caused by air escaping from leaking ducts.
If leaking air ducts are responsible for the hissing sound in your AC, you may also notice:
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Difficulty maintaining a cool home, as the conditioned air escapes into walls, ceilings, attics, basements, or crawl spaces.
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Increased energy bills, as your AC runs more frequently to compensate for the lost conditioned air.
Cause #4: Faulty Reversing Valve (Heat Pumps Only)
If you have a heat pump—an HVAC system capable of both heating and cooling your home—the hissing sound could be due to a malfunctioning reversing valve. This valve controls the flow of refrigerant, allowing the system to switch between heating and cooling modes.
When the reversing valve becomes faulty, it can get stuck between heating and cooling modes, which leads to a hissing noise. This is likely the issue if you also experience:
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Your system is not cooling your home as efficiently as before.
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Higher-than-usual energy bills.
You can learn more about the differences between heat pumps and AC systems in our blog.
Fixing AC hissing noise issues: What You Can Do About a Hissing Sound from Your AC
Unfortunately, you likely can't fix the AC hissing noise without calling a trained professional for help. We'll explain why for each issue:
Refrigerant leaks: You'll need the proper tools to not only locate the leak, which can be very small, but also to refill your system with the correct amount of refrigerant and properly pressurize it after the leak is fixed. Plus, AC refrigerant leaks can be harmful to the environment, since it's a chemical that only trained professionals should handle.
High compressor pressure: Since your AC compressor is pressurized, you'll need the right tools and know-how to properly pressurize your system to get it back to normal.
Leaky ducts: A professional will need to inspect your entire ductwork system and perform a duct sealing, which involves sealing any gaps, cracks, or disconnected joints in your ductwork. Since ducts are concealed in walls and ceilings, it's best to let a professional seal them.
Faulty reversing valve: A damaged reversing valve could be a sign that something else is wrong with your system, so it's important to have an AC tech inspect the valve to make sure nothing else is wrong with it. For example, if the valve has burned or oxidized parts, that's a sign the valve is overheating and may even require a new AC system.
Another reason it's best to let a professional diagnose hissing AC issues is that they can also inspect the rest of your system for underlying issues that could soon create more AC problems for you.
Observing Proper AC Maintenance
To help avoid AC breakdowns in the middle of summer, the best thing you can do for your system is to:
Keeping an eye out for any irregularities. If you notice anything out of the ordinary with your AC, contact a professional immediately to check it out. This helps prevent minor problems from becoming big, expensive ones down the road.
Maintain your AC regularly. This includes changing the air filter, keeping your AC clean and free of debris, making sure it always has good airflow, etc. If you don't want to have to think about maintaining your AC, you can sign up for a maintenance plan that includes annual service that helps keep your AC running as long as possible. Plus, you'll also get repairs included (depending on the plan), priority service, and more.
Need help fixing your hissing AC? Call Reliable Heating & Air at (770) 594-9969 or schedule an appointment for a free in-home estimate.
Since 1978, we've been offering the most reliable AC repair service in the Atlanta area. Our AC techs will inspect your AC to diagnose the hissing noise, then get your system back up and running as soon as possible.