Why is my AC making a hissing noise?

July 25, 2019

A hissing noise coming from your HVAC system is not something to be overlooked. Among the probable causes are leaky refrigerant lines, an internal valve leak or a serious problem with your compressor. If the hissing noise is coming from your ducts, then you could have leaking air ducts. This is annoying, but not necessarily a reason to worry. A hissing sound may be a sign for any of these things, but we’ll try to narrow it down a little 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 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 develops, you might hear a slight hissing sound as the refrigerant escapes via the leak. It escapes as a gas and can be a major health concern. If you notice signs of a refrigerant leak, power down the unit and call a qualified HVAC company to come evaluate the noise.

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 manage 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 tell if you’re looking for the cause. You need to maintain adequate pressure in your system for it cool your home, and leaks create additional health and mechanical problems. It’s best to get this fixed post haste if possible.

Are Hissing Noises Coming from the Compressor?

The compressor is located in the exterior air conditioning unit, which is also called a condenser unit. Listen quietly for the hissing noise. If the compressor is the issue, this could be an unsafe situation because it is a sign that the pressure in the compressor is too high. If you hear hissing, whistling, or shrieking coming from your compressor, shut off your air conditioner without delay and call a professional technician.

AC compressor located in exterior condenser unit 

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 turn on an air conditioner and cool your home sans compressor. The cost is variable based on factors such as 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 components are installed and won’t accept substitutes. While it’s impossible to provide estimates because of the variable costs, the expense is often big 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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