What Is An AC Suction Line – Everything You Need To Know

All across the country are air conditioner owners, but only a few are air conditioner experts. When it comes to AC suction lines, most people don’t know what they are.

However, this AC component is crucial for your AC’s cooling performance. Therefore, in this post, I want to share all the fundamentals you need to know about the AC suction line.

So, without further ado. Let’s get started!

What is an AC suction line?

what is ac suction line

There are two types of air conditioner refrigerant lines: suction line and liquid line. 

An AC suction line is the large copper pipe in charge of transporting refrigerant from the evaporator coil to the compressor. The refrigerant inside is gaseous with low pressure and temperature. It is also known as the vapor line or return line.

See also what an AC liquid line is.

How does a suction line work?

how does ac suction line work

Refrigerant plays an important role in the operation of air conditioners because this chemical can take away the heat in your house when turning from liquid to gas. After that, it can release the heat outside by turning itself from gas to liquid. This is basically why an air conditioner can cool your house down.

The refrigerant is liquid and cold before entering the indoor evaporator coil. When it passes through the evaporator, condensation will happen, and the heat in the air will be absorbed. During this process, the liquid becomes gaseous. 

Then the gaseous refrigerant needs to be sent to the compressor to be heated and compressed, and this is where the suction line comes into play.

The suction line carries gaseous refrigerant to the compressor to keep the refrigerant cycle working properly.

The suction line is cold, making it prone to sweating on summer days. As a result, adding foam pipe insulation to it is standard practice nowadays. On the contrary, liquid lines don’t always be wrapped with insulation.

Is the suction line the high or low side?

The suction line is on the low-pressure side. This is because the expansion valve has reduced the pressure of refrigerant before it gets into the evaporator. The pressure will remain at a low level when the refrigerant goes through the suction line later on.

If you want to locate the suction line near the outdoor unit, it would be the large pipe connected to the compressor from the top. 

Is the HVAC suction line cold or hot?

Again, the suction line is cold. This is due to the fact that the refrigerant passed through the expansion valve becomes really cold. Even though it will absorb a certain amount of heat in the evaporator, the temperature is still lower than the ambient temperature when it is in the suction line.

If you can’t tell which copper line is the suction line, you can get the correct answer by touching it.

How long does an AC suction line last?

AC suction lines are something long-lasting. Generally speaking, they can last more than ten years. However, its lifespan is decided by many factors, including the material, how you maintain it, and where you live.

Since it is filled with refrigerant (freon), it should be repaired or replaced by an HVAC technician. 

Signs of a problem with the AC suction line

As an air conditioning system consists of an array of components, it is difficult to tell which one goes wrong when your AC malfunction. There are some signs that may indicate that the suction line is the culprit.

1. Compressor overheating. When there is a restriction in the suction line, the compressor needs to work harder to suck the refrigerant, causing it to overheat.

2. Frozen evaporator or lines. This could be a sign that the suction line or liquid line is leaking. The evaporator is susceptible to freezing when there is a pressure change in the coils.

3. Poor cooling performance. Because the refrigerant cycle is impaired, your AC may provide less cooling than before. For example, your AC may not be able to cool below 80 degrees

As a side note, these conditions may also be caused by other components. You’d better hire a HAVC expert to inspect it. 

What can happen if a suction line is improperly sized?

Any suction line that comes with the air conditioner should be properly sized. Therefore, it is not a question you have to worry about in most cases. 

However, if you need to consider the sizing by any chance, you should keep in mind that using any improperly sized suction line is not recommended.

It will cause the compressor to work hard, and the refrigerant flows to decrease.

If the compressor often works at the maximum capacity, it will fail much quicker. As you know, replacing or repairing a compressor could be as expensive as getting a new AC unit.

Meanwhile, the reduced refrigerant flow will affect your AC’s cooling performance. It becomes useless if your AC can’t cool your house on scorching summer days.

In conclusion 

Until now, you have had a basic understanding of AC suction lines (HVAC suction lines). 

This copper line in the AC is an important part responsible for carrying gaseous refrigerant from the evaporator to the compressor. It is cold, and the tube is larger than the liquid line.

Since it is always covered with black foam insulation, you can easily tell it.

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Liz Yang is the founder of Airsmartly. She has been working at home for a few years and realizes that the performance of the HVAC system plays such an important role in our life. She has tested a lot of products in person, like humidifiers, air purifiers, dehumidifiers, and ACs, and wants to share tips about using or troubleshooting these products with you. Her uncle is an HVAC expert with over 30 years of experience in the field, and often offers assistance when she is unsure how to handle a situation. He is also in charge of reviewing the articles on this site.