Why is my AC making a hissing noise? 

A hissing noise inside your HVAC system should not be disregarded. Among the probable causes are leaking refrigerant lines, an internal valve leak or a serious failure with your compressor. If the hissing noise is coming from your ductwork, then you may have leaking air ducts. This is annoying, but not necessarily a cause for alarm. A hissing sound may 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 moments, you may not have any issues. That can be refrigerant in your expansion valve, which is part and parcel of the normal operation of your HVAC unit. 

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 develops, you might hear a slight hissing sound as the refrigerant escapes via the leak. Refrigerant escapes as a gas and can be a worrisome health concern. If you see signs of a refrigerant leak, shut down your HVAC and call a qualified HVAC company to come inspect the system. 

If the issue is a valve leak, it should be repaired by a professional 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 increase, which can be a sign if you’re looking for the cause. You must maintain proper pressure in your HVAC system for it cool your home, and any leak will create additional health and maintenance problems. It’s best to get this fixed quickly 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 within the compressor is too great. If you hear hissing, whistling, or shrieking coming from your compressor, switch off your air conditioner without delay 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 cycling refrigerant through the system. You cannot power on an HVAC system and cool your home without a compressor. The expense varies based on factors such as the type, unit size, and brand requirements. If you have a two stage compressor in your AC, you will 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 parts are installed and won’t accept substitutes. While it’s impossible to provide estimates because of the variable costs, the expense is often high enough to just do a replacement in older units. This is why it’s so important 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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