Why is my AC making a hissing noise? 

A hissing noise inside your HVAC system should not be overlooked. Among the possible causes are leaky refrigerant lines, an internal valve leak or a serious issue with your compressor. If the hissing noise is coming from your air ducts, then you could have leaking air ducts. This is annoying, but not necessarily a cause for alarm. A hissing sound could be a sign for any of these things, but we’ll try to narrow it down a little more. 

Does the hissing sound end after a few seconds? 

If you hear a hissing noise that stops after a few seconds, you may not have any issues. That might be refrigerant in your expansion valve, which is a part of the normal operation of your HVAC system. 

Is the AC Making a Hissing Sound with Bubbling Noises? 

Are you hearing a bubbling sound along with a hissing sound? This can indicate a refrigerant leak. If a refrigerant leak presents itself, you might hear a light hissing sound as the refrigerant escapes via the leak. Refrigerant escapes as a gas and can be a serious health concern. If you notice signs of a refrigerant leak, turn off your HVAC and call a professional HVAC company to come take a look. 

If the cause is a valve leak, it should be repaired by a professional as soon as possible. The job of the valves is to regulate the pressurization of the refrigerant gas and if unresolved, the leak will worsen. When it does, the hissing sound will sometimes grow louder, which can be a signal if you’re looking for the cause. You need to maintain proper pressure in your system for it run as intended, and any leak will create additional health and mechanical problems. You ought to get this fixed post haste if possible. 

Are Hissing Noises Coming from the Compressor? 

The compressor is located in the outdoor air conditioning unit, which is also called a condenser. Listen quietly for the hissing noise. If you find the compressor is the cause, this could be an unsafe situation because it is a signal that the pressure inside the compressor is too great. If you hear hissing, whistling, or shrieking coming from your compressor, turn off your air conditioner pronto and call an HVAC technician. 

Photo of AC unit showing location of compressor

Compressors are some of the most expensive units to repair or replace inside an air conditioner. Compressors are the part responsible for pushing refrigerant through the system. You cannot power on an HVAC system and cool your home without a compressor. The expense is variable based on factors like the type, unit size, and brand requirements. If you have a two stage compressor in your AC, you would need to replace it with another two stage compressor. It’s impossible to upgrade or downgrade the compressor type – your unit has specific requirements for what parts are installed and won’t accept substitutes. While it’s impossible to say how much a compressor replacement is because of the variable costs, the expense is often large enough to just do a replacement in older air conditioners. This is why it’s critical to shut off the air conditioning and call a reputable HVAC company if you hear hissing sounds coming from the compressor. 

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