“My AC Makes a Hissing Noise…Help!” Writes Bill in Rancho Cordova, CA

Bill in Rancho Cordova, CA is hearing some strange noises coming from inside his walls close to his AC unit. Bill asks:

“My AC seems to be working just fine but, every time it kicks off, it starts hissing so badly it sounds like a snake might have crawled into my walls. Now, I obviously know there’s not a snake back there, but I’m still worried about this sound. I’ve also heard it make a bubbling noise from time to time. My major concern here is that this is a precursor to a bigger problem. So, I want to know why my AC makes a hissing noise…please help!”

Bill, first of all, you’re right. There’s not an actual snake in your wall. Not one that’s hissing whenever the AC turns off, anyway. You’re also right about something else: that hissing noise that you’ve been hearing is definitely not something you want to ignore, especially not in the middle of summer with plenty of weeks of hot weather still to come. This hissing sound, plus that bubbling you hear sometimes, can actually have a few potential causes—and they are all ones that you want to address quickly.

Why Your AC Makes a Hissing Noise

Hissing is not a good sound to hear when you’re walking through tall grass in your bare feet. Equally, it’s not a good sound for Bill to hear coming from his AC unit or walls—we’ve established that. So, the next logical question would be why is your AC making a hissing noise?

Let’s take a look at some of the possible causes:

• Cause #1: The compressor is on the fritz. I’ve talked before about how to tell if your home AC compressor is bad, and one of the things I emphasized is that you should listen for odd noises, including hissing. A hissing noise from your AC could mean the pressure inside of your compressor is too high. Now, if that hissing starts to sound more severe, kind of like a high-pitched shriek, this is definitely a sign the pressure is too high. If you hear this, shut down your AC until you can have an HVAC professional take a look at this.
• Cause #2: Refrigerant is leaking. If a small refrigerant leak has developed inside your system, you may hear a light hissing sound. The bubbling (or gurgling) sound that Bill sometimes hears in his wall is also a strong indicator of a refrigerant leak. The hissing would be the sound of the refrigerant escaping, and the gurgling would result from it then mixing with oxygen. If I was working on Bill’s unit, this is one of the first things I’d check for. I would also caution Bill, and any homeowner who suspects they have this problem, to call a technician immediately because these chemicals can be hazardous.
• Cause #3: A valve is leaking. This is sort of related to the compressor as well in that the valve is connected to the compressor. If it isn’t sealed properly, it’ll admit a small hissing noise. See, these valves ensure that the refrigerant gas that cools air is kept pressurized. This is another issue that should be fixed quickly. If left unchecked, it has a tendency to get bigger, meaning that the AC will eventually work less effectively, or maybe even cease cooling your home’s air altogether.
• Cause #4: There’s an air leak in the ductwork. Now, this is a different sort of hissing noise from the other three since it will likely sound like it’s coming from the vents instead of from the actual unit. Hissing in the ductwork, though, can be just as serious as behind the wall because it means that there may be an air leak in either the supply or the return registers (the vents that pull warm air into your AC unit and blow cold air out). I’ve talked a lot about how leaky ductwork is both common and costly, so I won’t rehash it too much. But I will say that this kind of air seepage causes your AC to work harder than it should, which raises your bill and causes the unit to wear down and break faster.

How to Fix AC Hissing Noises

Once you have a decent idea of why your AC makes a hissing noise, it’s time to start figuring out how to fix it. The fortunate thing is that there isn’t a large amount of diversity in the causes of these sounds—it’s mostly leaks and pressurization—but all of them are a bit tricky to deal with on your own.

As I said above, I’d recommend calling a trained HVAC professional to come out and check out your AC if, like Bill, you’re hearing a hissing noise—both pressurization and chemical leaks can be dangerous, kind of like having an actual snake living inside your walls.

As I said above, I’d recommend calling a trained HVAC professional to come out and check out your AC if, like Bill, you’re hearing a hissing noise—both pressurization and chemical leaks can be dangerous, kind of like having an actual snake living inside your walls. Pressurization can cause pieces to shoot off your air conditioner at high speeds if handled incorrectly, and refrigerant leaks can send dangerous chemicals spilling out of your HVAC unit. For your safety, as well as the long-term well-being of your air conditioner, I’d suggest calling out a trained professional to handle these hissing hiccups.

So yes, Bill, you should rest easy that you don’t have a black mamba or a rattlesnake crawling around in your HVAC system. But, don’t rest too easy. When your AC makes a hissing noise, it could mean that there’s a major problem brewing, one that might get worse if you don’t get it fixed. I’d suggest putting in a call to a local professional for a check-up sooner rather than later.

I don’t need to tell Bill that Rancho Cordova, like the rest of Northern California, is still going to be pretty hot for at least a few more weeks, if not longer. The last thing a homeowner wants with all this heat still ahead of us is an air conditioner that can’t be relied on. If it goes out, I have a feeling that it’ll be the homeowner sitting around making hissing noises of their own.

Don’t ignore the hissing noise that your AC unit is making. Contact Bell Brothers today to have trained professionals come take a look.

Image courtesy Unsplash user Nathan Fertig