What Do Air Conditioner Hissing Sounds Usually Mean?

Your air conditioner is a machine with many moving parts. As such, it’s natural for it to make a bit of noise while it operates. However, unusual or bothersome noises, such as loud hissing and clunking, can signify deeper problems. If you notice your air conditioner hissing when it’s off, always contact a professional right away! 

That being said, not every air conditioner hissing noise warrants an emergency inspection or repair. In this post, we’ll help you identify the ones you should worry about and the ones you can leave alone.

Refrigerant Leak

A refrigerant leak is one of the most common causes of air conditioner hissing, and it’s also one of the most problematic. Not only can your air conditioner not cool your home without refrigerant, but it can even end up heating air in your home instead. Warm air from your vents is one sign of a refrigerant leak, but the hissing noise may be the first symptom you notice. 

Since the refrigerant in your AC system is constantly under pressure, it tends to make an audible hissing noise when it depressurizes. You’ll hear this hissing even when your AC unit is turned off. It may also make bubbling and gurgling noises in addition to the hissing, and you may notice frost and ice forming on your refrigerant pipes or your outdoor AC unit leaking water. 

If your air conditioner doesn’t seem to be in top shape—if it’s running more than usual, for example, or you have unusually high energy bills—this is another nail in the coffin for a refrigerant leak. If you see these warning signs, you should make an appointment with an AC repair professional right away. 

While air conditioner hissing may seem like a mild annoyance in the moment, it’s essential to address the cause right away. If your air conditioner is running more than usual, the added strain could eventually burn the motor, fan, or condenser, leading to costly repairs. Plus, air conditioner refrigerants can pose serious health hazards to all residents of your home. 

A reputable HVAC technician will be able to educate you on whether you’re better off repairing or replacing your AC unit after a refrigerant leak. 

High Compressor Pressure

Most air conditioners use a compressor that moves pressurized refrigerant through their systems. If your compressor becomes compromised somehow, such as when it has a leak or when pressure builds up too high, that escaping pressure could create a high-pitched hissing noise. 

However, most newer air conditioners have a system failsafe that will turn the AC off if the pressure rises too high. In this case, you likely won’t hear a hissing noise at all—the unit will just turn itself off instead. In either case, the best solution is to turn your air conditioning off and call a professional for help.

Malfunctioning Heat Pump Valve

Air conditioners aren’t the only HVAC component that can cause hissing. Heat pumps can also create persistent and annoying noises that sound similar to an air conditioner hissing. Usually, this happens when the reversing valve in your heat pump stops working or gets stuck. 

Heat pumps work by pumping heat in or out to change your home’s temperature (hence the name). When it switches from one mode to another, the whole system changes directions using the reversing valve. If that valve stops working, you’ll hear an uninterrupted hissing noise outside your home.

Leaky Ducts

In some cases, the source of the hissing in your home may not be from the air conditioner at all. If you only hear a hissing noise when your HVAC fan runs, then it could be your ducts leaking from a small hole instead. The size and shape of the hole can affect the way this hissing sounds. 

It can be tough to pinpoint the source of duct-related hissing noises, especially if the problem is deep inside your walls somewhere. However, if the source hole is exposed, such as in an unfinished basement, you may be able to track down the noise and patch it yourself. 

For the most part, leaky ducts don’t pose any threat to you or your home, though the hissing noises they create can undoubtedly be a nuisance.

Thermostatic Expansion Valve Operation

Fortunately, some air conditioner hissing noises are completely normal. Your thermostatic expansion valve, for example, is a part of your AC that helps relieve refrigerant pressure. It normally lets off quiet hissing noises as it does its job, and you’ll usually hear these noises indoors. 

If you hear this noise intermittently, you shouldn’t have anything to worry about. However, if you hear the noise constantly or it changes in pitch to screeching or whistling, you should contact a professional for assistance.

Why You Should Contact a Professional

Even if your air conditioner is in perfect health, it’s always a good idea to have it inspected by an HVAC professional regularly. A professional may be able to identify and repair minor problems before they turn into expensive issues. If you’re fearful of costly repair bills, the best way to prevent them is to contact your local HVAC repair technicians early and often. Don’t wait until a small issue grows into a problematic repair or replacement! 

Additionally, you should never try to repair your air conditioner yourself if it starts hissing unexpectedly. Air conditioner refrigerants can be hazardous, and no known drugs can counteract the effects of refrigerant poisoning. Plus, fixing an air conditioner is illegal if you’re not properly certified, so this is never something you should attempt yourself! 

If you’ve experienced unusual nausea, vomiting, dizziness, and headaches around the same time as you’ve noticed your air conditioner hissing, contact a professional right away! Prompt action doesn’t just protect your health—it saves your wallet, too. 

When you’re ready to call in the pros, consider air conditioning repair by Inland Empire Comfort. Our trustworthy technicians will get to the bottom of the issue efficiently and affordably. Contact us at (951) 336-8709 today to set up an appointment.