Your faithful AC has been doing a great job cooling down your home so far, but then suddenly you hear a strange hissing noise coming from your AC unit when it shuts off.
A hissing sound from your AC can possibly indicate a serious problem, so you’ll want to identify the cause as quickly as possible. Below we’ll take a look at a few possibilities for what may be causing your AC to make a hissing sound.
Why Is My AC Making A Hissing Noise?
1. Low or leaking refrigerant
This is one of the most common causes of a hissing air conditioner unit. The refrigerant gas used for cooling is either low or is currently leaking out.
This refrigerant is held under pressure within the AC unit, so when the unit turns off and depressurizes, you will hear the hissing noise.
Other noises such as bubbling or gurgling sounds can also accompany the hissing as it gets worse.
2. Faulty valves
The inside of an AC unit or heat pump contains valves that deal with changing pressures or even reversing directions of airflow. If these valves start to fail, you will start to hear hissing noises as gasses and air leak out when they’re not supposed to.
With heat pumps, this can result in an uninterrupted hissing noise as the unit shuts off. As time goes by, these hissing noises can become more high pitched. If this starts to happen it’s generally the sign of a major problem that needs addressing.
3. High compressor pressure
A hissing noise may be the result of the compressor in your AC unit running at too high of a pressure. Some modern AC units have ways to detect this high pressure and will simply turn off before any further damage can be done to the unit.
But for older models, you may hear a hissing noise if the compressor is faulty or running at too high of a pressure. Not addressing this issue can lead to further damage.
How Do I Fix The Hissing Sound In My Air Conditioner?
Fixing the issues that can be causing your AC unit to make a hissing noise often requires a professional. Some of these repairs can be relatively inexpensive, while some are more costly
1. Recharge the refrigerant in your AC
In most cases recharging your AC unit with refrigerant will require professional service from a qualified technician.
Although in some areas they do sell DIY kits for this purpose, it is not advised unless you’re experienced.
Recharging the AC with refrigerant may solve the problem for a short while, but if there is a leak the hissing noise will likely return when the gas returns to lower levels.
2. Repair the faulty valve
This type of repair will also require professional service by a qualified technician. Troubleshooting the faulty valve and replacing it may be beyond the skills of most DIY homeowners.
However, it is not impossible if you feel your skills are adequate.
3. Compressor repair
If the compressor needs to be replaced, this is one of the costliest of the repair options when it comes to fixing an AC unit. Such a repair requires the tearing down of the whole unit, replacing the part, then recharging the unit.
The cost of the compressor is also one of the more expensive components within the AC unit. So if the unit is old or has other issues besides the hissing, it may make more sense to just replace the entire AC.
Air Conditioner Making Hissing Noise FAQ
Is it normal for AC to hiss?
No, your AC should not be making any extended hissing sounds after it shuts off or even while running. You may hear some very brief start-up noises or shut-down sounds and those are perfectly fine. But any long hissing is the sign of a problem.
If the hissing progresses to a high pitch whining, then you should turn off the unit immediately and schedule a service check.
Why is my HVAC hissing?
If your HVAC is hissing, it’s almost always either an issue with leaky or low refrigerant or an internal component of the AC is faulty. The faulty component is generally the compressor or a valve.
Make sure the hissing isn’t coming from any ductwork, as sometimes a leak or hole in the ductwork can mimic the sound of an AC hissing. In this case, simply repair the hole in the ductwork.
Holes or leaking ductwork can also cause your AC to run more often than it needs to, leading to excessive wear and breakdowns. So even though repairing these holes is a minor repair, it can help prevent larger repairs down the road.
AC compressor hissing after shut off
If your compressor is hissing after shutting off, it means there is a leak or the compressor is failing. Having the AC unit serviced as quickly as possible may prevent more damage, so it’s important to call a service technician as soon as possible.
An AC compressor is one of the more expensive components to replace, so if you suspect an issue with the compressor, it’s best to get it looked at immediately.
Can you hear Freon leaking from an AC unit?
Most leaks of Freon or refrigerant will not be audible. Although leaking may lead to hissing noises or gurgling noises when the AC unit shuts off.
Any noises such as this indicate there is a problem somewhere in your AC system and you should consult a qualified technician to troubleshoot the problem and avoid an even costlier repair.
Final Words About Hissing Noise From AC
Hissing noises coming from any AC unit or HVAC is not normal and most likely indicates a problem. Following the tips in this article should help you narrow down the possible causes and eliminate any simple issues causing the hissing.
Keep in mind that many of these problems may require a service technician, and getting your hissing AC unit checked soon may prevent more damage from occurring.