Although today's air conditioning systems are designed with quiet performance in mind, they still make a negligible amount of noise. However, certain noises can signal the start of malfunctions that could potentially sideline your A/C system if they're not caught early on. If the gentle hum of your A/C gives way to a hissing sound, there may be a problem that needs to be addressed as soon as possible.
Periodic Hissing Noises
If you hear hissing noises at regular intervals with each interval lasting for only a few seconds, don't worry -- it's just the A/C system's expansion valve operating normally. The expansion valve plays a crucial role in transforming incoming high-pressure liquid refrigerant into a low-pressure vapor form, primarily by regulating the amount of refrigerant that flows through the valve. As a result, you may hear a brief hissing sound at regular periods as your A/C system operates. These sounds are normal and nothing to worry about, in most cases.
Continuous hissing noises can indicate a number of issues going on with your home's A/C system. For starters, it could be the sign of a refrigerant leak somewhere within the A/C unit. The various refrigerant lines throughout your unit can develop pinhole leaks due to corrosion or unintentional damage. As high-pressure refrigerant forces its way past the point of leakage, it can create a hissing noise that won't let up until the system is empty. A refrigerant leak is bad news since your A/C system needs a certain amount of refrigerant to properly function without causing further damage.
If the noise is coming directly from the compressor, the internal refrigerant valves could be to blame. If these valves are damaged or fail due to wear or age, it can cause a loud hissing sound as the A/C system runs. According to Inspectapedia, the hissing noise usually dies down when the system is shut off and the high and low side pressures within the compressor are given a chance to equalize.
Excessive internal pressures within the compressor can also cause hissing noises. In some extreme cases, the excess pressure can turn the hissing into a screaming sound. You should shut down your A/C system the instant you hear any screaming noises, since running the compressor in this state could damage other parts of your A/C system.
You might also want to check the vent registers. A loose or ill-fitting register can allow air to escape through the edges of the vent, creating a hissing noise that increases or decreases in intensity depending on your A/C system's fan speed.
Solving the Problem
Hissing noises that originate from your vent registers can be fixed by refitting the offending register and sealing it with silicone caulk or mastic sealant. If possible, you should also take this time to check the rest of your home's ductwork for any signs of damage, as well as gaps and poor sealing.
Hissing noises that come directly from within your A/C system, on the other hand, should be dealt with by your HVAC technician instead. If the compressor or refrigerant lines need to be replaced, the refrigerant has to be removed and stored until the repairs are finished. Only your HVAC technician has the tools and training to safely remove, store and add refrigerant to your A/C system.
It's also good idea to have your HVAC technician inspect the rest of the A/C system to ensure that there aren't any other problems lurking in the shadows. By keeping a close eye on your A/C system, you can help prevent hissing sounds and other strange noises from making a comeback. For more information, contact local HVAC companies like Elite Heating, Cooling and Plumbing.