A hissing AC or other alarming noises could mean your HVAC system is creating pressure conditions that make it unsafe to keep running. When your AC is making strange noises, we always recommend turning off your system and calling a professional to diagnose the problem.
If your AC is making a hissing noise, the problem could be:
Refrigerant leaks
High pressure in the compressor
Leaking air ducts
Faulty reversing valve (heat pumps only)
We'll go over each issue and what you need to do to fix it. We'll also walk you through how to keep an eye out for signs of AC problems to prevent catastrophes like this from happening at the worst times—like the middle of a Georgia summer.
Need a professional to diagnose why your AC is hissing? Call Reliable Heating & Air at (770) 594-9969 or schedule an appointment.
We have more than 200 trucks and 300 technicians on the road, which means we'll get to your home fast to diagnose the AC hissing noise and repair your AC.
Cause #1: Refrigerant Leaks
Refrigerant leaks are the most common cause of a hissing AC. If your AC has a refrigerant leak, you may hear a hissing or bubbling noise coming from the compressor in your outdoor unit. Since the system is pressurized, the hissing sound happens when it loses pressure due to a refrigerant leak—if the leak is large enough.
The hissing in your air conditioner is most likely caused by a refrigerant leak if you also notice:
Vents blowing warm air
Energy bills that are higher than normal
Cause #2: High Pressure in Compressor
The compressor is the part of your AC that moves refrigerant through your system. The compressor is pressurized, which means it can make a hissing or screeching sound in the outdoor unit if it has too much pressure.
Built-up pressure in the compressor is likely the problem if you notice:
The screeching/hissing sound starts when the AC kicks on and lasts for 10-15 seconds.
Your system starts and stops more than usual.
Cause #3: Leaking Air Ducts
Over time, your AC air ducts can deteriorate and develop gaps, cracks, or tears that air will escape through. Many Fayetteville homeowners say they hear a hissing or high-pitched whistling sound from their vents, which is caused by the force of your AC ducts leaking air.
Leaky ducts are likely causing the hissing sound in your AC if you also notice:
Difficulty keeping your home cool, since the conditioned air is escaping into places like your walls, ceilings, attics, basements, or crawl spaces.
Increased energy bills, since your AC is running more trying to compensate for conditioned air escaping the ducts.
Cause #4: Faulty reversing valve (heat pumps only)
If you have a heat pump, which can cool and heat your home, instead of an AC, which can only cool your home, the hissing sound could be the reversing valve. The heat pump reversing valve is responsible for switching the flow of refrigerant that allows it to heat and cool your home.
When this reversing valve goes bad, it can get stuck between heating and cooling mode, causing a hissing noise. This is likely the issue if you also notice:
Your system isn't cooling your home as well as normal
Energy bills that are higher than normal
You can learn more about the differences between heat pumps and AC systems in our blog.
Fixing AC hissing noise issues
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.