Air Conditioner Making A Hissing Noise?

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Updated September 16, 2022

Even with a top-rated air conditioning unit, you will occasionally hear it make a hissing noise. So, if you’re wondering, “Why does my AC hiss?” read on.


  • It is usual for an air conditioner to occasionally and momentarily hiss or whine, especially during the sweltering summer heat.
  • Loud and continuous hissing might be gaseous refrigerant escaping your AC system.
  • If the pressure in your AC compressor gets too high, you will hear a hissing or shrieking noise from the outdoor unit.

While short instances are to be expected, prolonged hissing is unusual and might require professional repair. Fortunately, you can tentatively diagnose this air conditioning system issue by looking for some key signs discussed below.

Insider Tip

Always contact an air conditioning expert to diagnose a lousy compressor and check refrigerant levels.

But before we continue, since hissing noises are sometimes the result of a refrigerant leak, consider learning what causes air conditioner refrigerant leaks. For example, regular maintenance can prevent issues such as buzzing or bubbling sounds and frozen refrigerant lines. You may also want to read up on the types of motors in an AC system for more context on AC maintenance.

Of course, unlicensed people cannot legally handle AC refrigerant, so contact a professional technician for a refrigerant charge if needed.

Common Causes of Hissing Noises in AC Units

Hissing air conditioning noises are a genuine cause for concern, but it doesn’t always call for expensive repairs. For example, occasional and quiet hissing noises are typical for an AC system, especially during a hot day in summer. However, if this strange sound gets louder or doesn’t stop, it could indicate that you have a severe issue.

Refrigerant Leaks

Refrigerant leaks are a common AC problem, but the concern goes beyond the hissing noises. Without refrigerant, your AC system cannot cool your home, and you may feel warm air from your air vents.

Since an AC system uses pressurized gases, you may hear hissing as gas refrigerants escape due to an internal valve leak. You might also hear gurgling or bubbling noises.

A refrigerant leak is not a problem you can fix on your own. Contact a licensed AC professional if you think your unit is leaking refrigerant.

Faulty AC Compressor

In a central AC system, the compressor is in the outdoor unit, also called the condenser unit. The compressor pushes refrigerant through the system and makes cooling possible.


If you frequently need to top off your refrigerant levels, this is a sign of a refrigerant leak and requires immediate attention; ignoring the issue can jeopardize the entire unit and your health.

Hissing or a high-pitched whistling sound is an indication that the compressor is leaking or that the pressure is too high. You should immediately turn off your AC if you think you have a compressor leak because it can be hazardous.

It is possible to repair a bad compressor. However, if it has sustained extensive damage, you may find replacing your AC is cheaper than fixing it.

STAT: According to a 2020 US EIA (Energy Information Agency) survey, about 18% of Americans set their AC system to 69 degrees or less. (source)

Why Does My AC Hiss FAQs

I think I have a refrigerant leak. Should I repair or replace my AC?

A coolant leak is a serious issue that will prevent your AC from adequately cooling your home, so the unit needs to be repaired or replaced. If your repairs exceed the cost of a new AC unit, it’s recommended that you buy a new model. In addition, if your unit is near ten years old, you shouldn't pay for anything other than low-cost repairs, as EnergyStar recommends replacing an AC unit every 10-15 years.

How often should I replace an AC air filter?

You should change your air filter every three months (or 90 days) to keep the system at peak efficiency. That said, if you have a multi-person home, indoor smokers, or pets, it’s best to replace your air filter every month.

Is air conditioning refrigerant toxic?

Most AC units use refrigerants called Freon or Puron, and they are generally safe to handle for licensed AC technicians. Keep in mind, however, that gaseous refrigerant is tasteless and scentless and can cause serious health effects in large amounts. The symptoms of refrigerant poisoning include swelling in the throat and sinuses, difficulty breathing, and other health issues.
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