Why Is My AC Refrigerant Line Sweating? – How To Stop It?

How bizarre! There is a puddle of water on the floor, and you find that it is because your air conditioner refrigerant line is sweating.

Don’t worry, you are not alone. All across the country are people who face the same problem. 

In short, it is normal for a suction line to sweat, but it is also a sign that the insulation is broken. If that occurs in a liquid line, it may mean that the refrigerant is leaking or the drier is clogged.

However, there is much more than that. I will detail all the information you need to know about the causes and fixes of an AC refrigerant line sweating in this post, so keep reading!

Why is my AC line sweating?

AC refrigerant lines, also known as AC lines, AC pipes, and AC copper pipes, are lines in charge of transporting refrigerant.

If you are looking for why an AC condensate line is sweating, check here.

Since there are two types of AC lines – suction line and liquid line, I want to explain the causes of sweating based on the type.

Suction line sweating

ac line sweating lack insulation

The suction line is the large copper pipe that connects the evaporator coil to the compressor.

As you may know, the refrigerant becomes very cold when it passes through the expansion valve.

Even though it will absorb a certain amount of heat when passing through the evaporator coil, the temperature is still low when it comes out from the evaporator and enters the suction line.

That is to say,  the refrigerant in the suction line is cold, as is the surface of the line.

Like the condensation on the cup of iced soda, you will also see condensation on the suction line.

This is due to the fact that when the hot air makes contact with the cold surface, its temperature may fall below the dew point, and the water vapor may turn into liquid water.

As a result, AC suction line sweat is normal. However, because this is a common occurrence, HVAC professionals may have warped it with foam insulation to prevent it from happening. It’s just a standard practice these days.

If the suction line still sweats when insulated, its insulation may be damaged.

Liquid line sweating

Contrary to suction lines, liquid lines are smaller and much warmer, even though they are also made of copper. 

This type of AC line transports liquid refrigerant from the condenser to the expansion valve. While the refrigerant temperature drops to some extent in the condenser coil, it is still quite hot. 

It means that the liquid line is warm, preventing condensation from happening. If you see condensate on the liquid line, it is likely a sign that something is wrong with your air conditioning system.

There are four primary causes why your AC liquid line is sweating:

1. Refrigerant leak

The refrigerant level will not change under normal conditions. When there is a leak, the pressure drops, causing the temperature of the AC liquid lines to drop.

When the liquid line temperature falls below the ambient temperature, it begins to sweat.

2. Clogged AC drier 

Most air conditioning units nowadays have a drier between the compressor and expansion valve to remove the moisture inside the coil. When it is clogged, it will lower the pipe’s temperature, resulting in sweating on the surface.

3. Frozen evaporator coil 

When the evaporator coil is frozen, it will impact the normal circulation of the freon, causing a lower temperature on liquid lines. Dirty filters and coils, as well as malfunctioning blowers, can make an AC to freeze.

4. Refrigerant migration in winter

Occasionally, you may see your AC liquid lines sweat in winter months, even if your AC is not running. 

This is because refrigerant tends to accumulate in the compressor, and the crankcase heater inside will push a part of the refrigerant out of the compressor and allow it to get into the liquid line.

In this case, the gaseous refrigerant in the liquid line will absorb the heat in the ambient air, and condensation will form on the lines. In other words, the liquid line turns to be evaporator coil.

How do I stop my AC copper pipe from sweating?

Until now, you have figured out all the common reasons why your AC lines are sweating, let’s jump to the possible fixes. 

Replace insulation

Again, suction lines are often wrapped with foam insulation. If it sweats, it means that you need to replace the insulation. Luckily, it is inexpensive and easy to do.

Check here to learn how to insulate AC lines correctly

Once the insulation is added, the sweating will stop automatically.

Fix the leaks

Refrigerant leaks can happen at both suction lines and liquid lines. However, you are not allowed to fix it yourself. As the refrigerant is hazardous, it should be done by a certified HVAC expert.

When the pressure of the refrigerant returns to normal, your AC pipes will not sweat.

Replace the drier

Rather than repairing it, you should replace the drier when it is clogged. Because it is connected to refrigerant lines, you should leave this task to a pro.

Cut off the power of the outdoor unit when not in use

If you want to avoid the copper pipe sweating on cold days, you’d better turn off the outdoor unit completely by turning off the breaker. This way, refrigerant migration will stop.


Don’t be alarmed if your AC lines start to sweat. In most cases, replacing the foam pipe insulation will stop it.

If it happens to the liquid line, it could mean that the refrigerant level is low, the drier is clogged, or you forgot to turn off the outdoor unit, all of which should be addressed by a certified professional.

Hopefully, this guide has assisted you in identifying and resolving the sweating problem on the AC copper lines.

About The Author

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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 dozens 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.

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