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8 Reasons Why Your AC Is Making a Hissing Sound

Having an efficient AC unit is essential to your comfort in Concord, NC, especially during the summer. If you hear a hissing sound, the cause could be an issue in any one of several components. It can signal that something is inefficient or your AC is struggling to operate properly, requiring a quick AC repair. Here are 8 possible reasons why your AC is making that noise and what it means for you.

1. Refrigerant Leak in Coil or Line

One of the most common causes of hissing sounds coming from an AC unit is a refrigerant leak in the coil or line. Refrigerant is important for absorbing the heat from your indoor air while in the evaporator coil. If there is a leak, it usually first appears in the evaporator coil, the cause of which is erosion from formic acid and formaldehyde.

Sometimes, the leak may instead be in the refrigerant lines, which are two copper lines that connect your outdoor AC unit or heat pump to the indoor evaporator coil. The larger line, also called the suction, return, or vapor line, is insulated and carries a cool gas.

2. High Compressor (Condenser) Pressure Leak

Another cause of an AC hissing sound is a high compressor pressure leak. The compressor is inside the outdoor unit and is one of the most expensive internal AC components to replace, as it pushes refrigerant through the system. In this case, it means the pressure inside the compressor is too high and hazardous to keep running.

3. Air Duct Leak

An AC hissing sound could mean a leak in your air ducts, which normally direct the path of airflow throughout your home. Leaky air ducts result in unwanted or uneven airflow. You may also experience excessive dust.

4. Weld Joint Leak

Wear and tear of the weld joint can result in a leak and a hissing sound. Your AC has pipe weld joints at the ends of the coils, which are made of two different metals that serve to expand and contract at different rates. With wear and tear from pressure, these joints eventually have microscopic cracks that can leak refrigerant.

5. Faulty U Joint

The universal joint allows for the transfer of motion within your AC unit. If it’s faulty, it can cause a hissing sound and make cooling your home less efficient.

6. Schrader Valve Leak

A leak in the Schrader valve (also called the service valve, core valve, or American valve) can cause a hissing sound as it fails to prevent air from getting into the refrigerant. Debris can get stuck under its spring mechanism and prevent the valve from closing properly. Alternatively, its rubber o-ring can deteriorate over time.

Either one can result in a leaky Schrader valve. When this happens, the air in the refrigerant will cause the condenser surface area to reduce and result in high condensing pressure. This means you will have an undercharged system.

7. Faulty Expansion Valve or Expansion Valve Leak

A faulty expansion valve or expansion valve leak may be the cause of your AC hissing sound, meaning it can no longer control the amount of refrigerant your AC needs. A compressor failure can cause a “bad” expansion valve since it cannot transfer the necessary amount of refrigerant to the expansion valve, resulting in a valve leak.

Another cause of an expansion valve leak is filling with the wrong amount of refrigerant. Whether it is underfilled or overfilled, your valve will have limited function for cooling your home.

8. Faulty Reversing Valve (Heat Pump Only)

If you have a heat pump, a hissing sound could mean a faulty reversing valve. This component reverses the flow of refrigerant so your heat pump can release the heat indoors rather than outdoors. If it is faulty, it means there is not enough refrigerant to properly cool the air.

What Should You Do If Your AC Is Making a Hissing Sound?

When your AC has been making a hissing sound, you’ll want to turn it off and call an HVAC technician for repair of either of its components or an AC replacement if it’s too late. It is especially important to do so immediately as it could be a refrigerant leak, which is hazardous to health, or a high condenser pressure leak, which could result in needing replacement.

Contact Trustworthy AC Professionals for Your Cooling Needs

It’s important to remember that a hissing sound coming from your AC is normal if it lasts only a few moments. Such a sound occurs during normal operation, but it should not continue.

When you need fast assistance, we at All Temp Co., Inc Air Conditioning, Heating, Plumbing, & Electrical in Concord, NC are here as your local HVAC technicians. You can rely on us to bring you efficient, safe, durable cooling with the best products we have to offer, whether you need AC repair or replacement. We pride ourselves on our transparency and the genuine relationship we have with our customers. Contact us today to learn more about our AC services.