Why is my AC making a hissing noise? 

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

Does the hissing sound stop after a few seconds? 

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

Is the AC Making a Hissing Sound with Bubbling Noises? 

Are you hearing a bubbling sound paired with a hissing sound? This could indicate a refrigerant leak. If a refrigerant leak is present, you might hear a slight hissing sound as the refrigerant escapes from the leak. It escapes as a gas and can be a serious health concern. If you notice signs of a refrigerant leak, turn off the unit and call a professional HVAC company to come take a look. 

If the issue is a valve leak, it should be repaired by a qualified technician as soon as possible. The job of the valves is to help with the pressurization of the refrigerant gas and if unresolved, the leak will worsen. When it does, the hissing sound will often intensify, which can be a tell if you’re looking for the cause. You must maintain proper pressure in your system for it cool your home, and leaks create additional health and mechanical problems. You want to get this fixed quickly if possible. 

Are Hissing Noises Coming from the Compressor? 

The compressor can be found in the exterior air conditioning unit, which is also called a condenser unit. Listen quietly for the hissing noise. If the compressor is the problem, this could be a dangerous situation because it is a sign that the pressure in the compressor is too much. If you hear hissing, whistling, or shrieking coming from your compressor, power down your air conditioner immediately and call an HVAC technician. 

Photo of AC unit showing location of compressor

Compressors are some of the most pricey units to repair or replace inside an AC. Compressors are the part responsible for circulating refrigerant through the system. You cannot power on an HVAC system and cool your home without a compressor. The expense changes based on factors like the type, unit size, and brand requirements. If you have a two stage compressor in the unit today, you would need to replace it with a two stage compressor. It’s not possible to upgrade or downgrade the compressor type – your unit has specific requirements for what compressors are installed and won’t accept substitutes. While it’s impossible to give a quote online because of the variable costs, the receipt is often large enough to just do a replacement in older ACs. This is why it’s crucial to shut off the air conditioning and call a reliable HVAC company if you hear hissing sounds coming from the compressor. 

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