Why is my AC making a hissing noise? 

A hissing noise coming from your HVAC system is not something to be ignored. Among the potential causes are leaky refrigerant lines, an internal valve leak or a serious issue with your compressor. If the hissing noise is coming from your ducts, then you might have leaky air ducts. This is annoying, but not necessarily something to panic over. A hissing sound may indicate any of these things, but we’ll try to narrow it down a little further. 

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 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 paired with a hissing sound? This can indicate a refrigerant leak. If a refrigerant leak develops, you may hear a light hissing sound as the refrigerant escapes through the leak. It escapes as a gas and can be a major health concern. If you see signs of a refrigerant leak, shut down your HVAC and call a qualified HVAC company to come take a look. 

If the problem is a valve leak, it should be repaired by a professional as soon as possible. The job of the valves is to manage the pressurization of the refrigerant gas and without repair, the leak will worsen. When it does, the hissing sound will often intensify, which can be a sign if you’re looking for a cause. You need to maintain proper 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 quickly if possible. 

Are Hissing Noises Coming from the Compressor? 

The compressor is found in the outdoor air conditioning unit, which is also called a condenser unit. Listen around here for the hissing noise. If it turns out that the compressor is the problem, this could be a dangerous situation because it is a sign 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 immediately and call an HVAC technician. 

Photo of AC unit showing location of compressor

Compressors are some of the most costly units to repair or replace inside an air conditioner. Compressors are the part responsible for circulating refrigerant through the system. You cannot run an AC and cool your home without a compressor. The pricing changes based on factors like 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 impossible to upgrade or downgrade the compressor type – your unit has specific requirements for what compressors are installed in order to operate safely. While it’s impossible to say how much a compressor replacement is because of the variable costs, the expense is often large enough to consider a replacement in older units. This is why it’s crucial 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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