Why is my AC making a hissing noise?
A hissing noise coming from your HVAC system should not be ignored. Among the probable causes are leaky refrigerant lines, an internal valve leak or a serious issue with your compressor. If the hissing noise is coming from your ductwork, then you could have leaky air ducts. This is annoying, but not necessarily a reason to worry. A hissing sound may indicate any of these things, but we’ll try to narrow it down a little 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 issues. That could 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 paired with a hissing sound? This can indicate a refrigerant leak. If a refrigerant leak is present, you might notice a slight hissing sound as the refrigerant escapes via the leak. The coolant escapes as a gas and can be a serious health concern. If you notice signs of a refrigerant leak, turn off your HVAC and call a expert HVAC company to come evaluate the noise.
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 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 signal if you’re looking for a cause. You need to maintain proper pressure in your HVAC system for it run as intended, and leaks 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 can be located in the outdoor air conditioning unit, which is also known as a condenser unit. Listen nearby the condenser for the hissing noise. If the compressor is the issue, this could be a dangerous situation because it is an indication that the pressure inside the compressor is too high. If you hear hissing, whistling, or shrieking coming from your compressor, shut off your air conditioner immediately and call a professional technician.

Compressors are some of the most expensive parts to repair or replace inside an AC unit. Compressors are the part responsible for pushing refrigerant through the system. You cannot power on an HVAC system and cool your home sans compressor. The expense changes based on factors such as the type, unit size, and brand requirements. If you have a two stage compressor now, you will 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 and won’t accept substitutes. While it’s impossible to say how much a compressor replacement is because of the variable costs, the expense is often high enough to just do a replacement in older air conditioners. 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.