Why is my AC making a hissing noise?

July 25, 2019

A hissing noise inside your HVAC system is not something to be overlooked. Among the probable causes are leaking5 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 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 cease after a few seconds?

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

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 notice a slight hissing sound as the refrigerant escapes through the leak. Refrigerant escapes as a gas and can be a worrisome health concern. If you notice signs of a refrigerant leak, shut down the unit and call a professional HVAC company to come evaluate the noise.

If the cause 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 left alone, the leak will worsen. When it does, the hissing sound will sometimes grow louder, which can be a sign if you’re looking for a cause. You need to maintain adequate pressure in your system for it operate correctly, and any leak will create additional health and maintenance problems. It’s best to get this fixed post haste if possible.

Are Hissing Noises Coming from the Compressor?

The compressor is found in the exterior air conditioning unit, which is also known as a condenser unit. Listen quietly for the hissing noise. If the compressor is the cause, this could be a dangerous situation because it is a signal that the pressure inside the compressor is too much. If you hear hissing, whistling, or shrieking coming from your compressor, shut off your air conditioner immediately and call an HVAC technician.

AC compressor located in exterior condenser unit 

Compressors are some of the most pricey parts to repair or replace inside an AC unit. Compressors are the part responsible for circulating refrigerant through the system. You cannot run an AC and cool your home sans compressor. The cost changes based on factors such as the type, unit size, and brand requirements. If you have a two stage compressor now, you would need to replace it with another 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 can’t be MacGyvered. While it’s impossible to give a quote online because of the variable costs, the bill is often high enough to just do a replacement in older ACs. This is why it’s critical to shut off the air conditioning and call a trustworthy HVAC company if you hear hissing sounds coming from the compressor.

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