A hissing noise from your air conditioning unit is not necessarily something that needs to cause alarm, but you must ask a professional. There are several reasons that your AC unit makes a hissing noise.

The Compressor

One reason that your AC unit makes a hissing noise is because of the compressor. An air conditioner’s compressor is what makes the entire system run, and it contains refrigerant. Refrigerant is a cool liquid that has low pressure. When the compressor begins to work, it changes the refrigerant into a gas that has high pressure. The compressor also turns this high-pressure gas into a liquid again. As it cools the refrigerant, the air conditioning system can create cool air.

Without refrigerant, your AC unit would be unable to cool your house. If the refrigerant is at a low-pressure state, it is cool, and when it comes in contact with warm air, it lowers the temperature of the air. If the refrigerant is at a high-pressure state, it is hot, and when it comes in contact with cool air, it condenses. This causes the temperature to rise.

The description above takes place inside the outside unit of your air conditioning system in the condenser. This is where the compressor is located. Its purpose is to increase the refrigerant’s temperature and pressure so that the air can begin to evaporate as the temperature cools. This is when the air in your home becomes cooler.

The compressor may be the problem if you hear the hissing sound while you listen. When this occurs, it means that the pressure inside the unit is too high. When you hear a hissing noise that comes from your compressor, you must not run the air conditioner. This is the time to contact your AC technician.

The Refrigerant

A refrigerant leak is a very common cause of hissing noises. It may even occur when your air conditioner is not even running. Refrigerant is a chemical that expands or vaporizes, and in the process, it cools the area down. If you also hear a bubbling sound when you hear the hissing sound, it may be because the refrigerant is leaking. In this case, the refrigerant is escaping as a gas, so you must have a professional inspect your air conditioning system.

These sounds occur because the refrigerant leak is causing the system to lose pressure. If you see ice on your air conditioner, an increase in your energy bills or warm air coming from the vents, these are additional signs of a refrigerant leak.

The Air Ducts

Air ducts are pipes that allow air to travel throughout the house. They are connected to your air conditioner, where they filter the air, cool the air and then send it to the rooms in your house. Without proper maintenance, the air ducts develop tears, cracks or gaps that allow air to escape. If you hear hissing sounds coming from your vents, it may be because the air is escaping through the cracks. In this case, the hissing sound only occurs when your air conditioner’s fan runs.

With many places to escape, your air conditioner may not cool your home as efficiently because the cool air goes into your crawl spaces, basement, attic, ceiling or walls. When air escapes through cracks and gaps, the air conditioner must compensate and work harder to cool your home. The extra energy that this expends results in higher electric bills. If you have noticed that your electric bills are higher at the same time that you hear hissing sounds, leaky air ducts may be the reason.

The Expansion Valve

Your air conditioning system has an expansion valve. Its job is to regulate the pressure as it drops while the refrigerant goes from liquid to vapor. The expansion valve ensures that only a tiny amount of refrigerant can move into the evaporator coil at a time. This makes it possible for the refrigerant to freely expand into a vapor, and it causes the temperature to drop. The most important jobs of the expansion valve are to maintain the pressure in the evaporator, but it also helps refrigerant move into the evaporator so that your home can remain cool.

The expansion valve can also be the cause of the hissing sound. As the expansion valve operates, the refrigerant expands into a high-pressure state as hot gas. As it cools down, it returns to a liquid state at low pressure. This process creates a hissing sound that lasts several seconds, but these sounds occur at regular intervals. They may not necessarily mean that anything is wrong, but for peace of mind, you may want to have them checked by a professional.

The Vents

One or more of your air conditioner’s vents may be blocked or closed. Sometimes, people accidentally close their vents when they really should remain open. For example, you may have placed a piece of furniture over a vent without meaning to do so. Some people close these vents intentionally because they believe that closed vents will help the air conditioner work better. These actions do not have the effect that you are seeking. Instead, they cause hissing noises and other sounds because of the extra pressure on the air conditioning system. You must make sure that all of your vents are free and unobstructed so that the air conditioner can do its job as quietly as possible.

The Air Filter

The air filter fits into the air conditioning system. Its purpose is to clean the air, and it is necessary because the air inside your home may be dirtier than the outside air. You must have a good ventilation system to make sure that the contaminants do not build up on the inside. Along with protecting you and your family from contaminants, the air filter also keeps impurities from entering your air conditioning system.

The air filter is a screen that traps dust and other debris and keeps it from going into your air conditioning system and through your house. If too much time goes by before you change these filters, they become clogged and ineffective. They may also be the reason that you are hearing a hissing noise.

The Motor

When your air conditioner’s motor begins to have problems, it makes several types of sounds, and a hissing sound may be one of them. The best thing is to make an appointment with a technician so that he can determine whether or not your hissing sounds are issues.

When Is It Time to Take Hissing Noises Seriously?

Sometimes, the air conditioner makes hissing noises for a couple of seconds at a time. These are not necessarily sounds that are cause for concern. However, if the refrigerant leaks, you will hear constant hissing for a much longer time. When this occurs, this is something that you must bring to the attention of an AC professional. If you fail to address this hissing sound, it will only worsen, and you will be in danger of losing your cooling system.

At Express Plumbing Heating & Air, we can offer several HVAC services, including AC repair, AC maintenance and AC installation in Boise. If you also need our heating, plumbing or sewer services, we can arrange for our technicians to address those areas of your home as well. Call us today, and we will send a technician tomorrow.

Brad Jordan

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