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What Causes the Suction Line to Freeze Up?

By: Cody Dampf

October 10, 2024 3 min

Heat Pump

What is the Function of a Suction Line within an Air Conditioner?

Refrigerants have two copper lines that connect the indoor evaporator coil and the outdoor heat pump. The suction line is the larger tube that has insulation. It carries cool gas under low pressure from the indoor evaporator to the outdoor compressor. The suction line is also called the return or the vapor line.

The other line is usually smaller and uninsulated. It carries hot liquid under high pressure from the condenser to the evaporator.

Why Does The AC Suction Line Sometimes Freeze?

The suction line can freeze for many reasons. Read on to know the main ones.

Low Refrigerant

A refrigerant is a compound that changes from gas to liquid and vice versa as it regulates temperature in the house and helps your air conditioning system work properly. When the refrigerant absorbs heat from the house, it changes from low-pressure gas to high-pressure liquid. Then the high-pressure liquid travels outdoors where a fan blows hot air. As a result, it turns back into a low-pressure gas.

The refrigerant’s volume remains at the same level throughout the air conditioner’s life unless there’s a leak. A leak causes the pressure inside the copper tubes to reduce. A reduction in pressure causes a drop in the refrigerant’s boiling point and temperature.

Adding more refrigerant won’t help unless you find the leak and fix it.

When the refrigerant is low, its temperature at the beginning of the evaporator coil will be lower than the freezing point. The low temperature will cause the condensation inside the coil to freeze. Then, Ice builds on the coil and restricts airflow through the coil.

Without airflow to the coil, the refrigerant won’t absorb heat. So it will start to boil further in the coil leading to more freezing which continues up to the suction line.

Airflow Problems

If the filter gets dirty, it blocks airflow to the evaporator coil. Without airflow, heat doesn’t get to the evaporator coil, and the refrigerant doesn’t boil. As a result, the pressure and the temperature will drop, causing the system to freeze.

If the filter you’re using is too restrictive, it can cause the same problem. In this case, you’d have to replace the filter.

Also, the blower motor could stop working or run at a low speed due to worn-out bearings. An electric problem could blow up the motor, or the board could fail to supply current. This problem reduces the amount of air getting to the evaporator coil. The longer you let the system work without the motor, the more ice will accumulate on the suction line. Anything that blocks airflow to the evaporator coil can cause the unit to freeze.

Low Temperature

If the indoor temperature drops below 70F, the saturation temperature will also drop. And if it goes below 32F, the system will freeze. One reason why this might happen is if you set your thermostat too low. Most thermostats operate over 67F. If you set yours below that, it might cause freezing.

What You Should Do If Your Suction Line Freezes

If you notice frost on your suction line, check whether everything is running as it should. Check whether the motors are working and the fans are blowing air. If you don’t notice any problem, turn off the system to avoid causing further damage.

Remove the air filter and clean it to ensure the problem doesn’t result from blocked airflow. If the air filter is too restrictive or old, replace it. Keep in mind that many factors could cause the suction line to freeze. Sometimes the problem may be hard to detect. Instead of guessing what the problem is, call an HVAC professional to assist you.

You can ask your HVAC professional to install a freeze stat. This device monitors the temperature of the heat exchanger. If the temperature falls slightly above freezing, the freeze stat initiates a protective action and keeps the suction line from freezing.

How to Keep Suction Line from Freezing

Most problems with the HVAC system occur due to a lack of regular HVAC maintenance. If you don’t maintain your HVAC system, it will become inefficient. As a result, it will take longer to achieve the temperature you want in your house. Inefficiencies will also cost you more in power bills.

In addition, lack of maintenance can accelerate the rate of wear and tear and the HVAC components. If serious damages occur, you’d incur extra costs in replacing those damaged components. So it’s highly recommended that you have an HVAC professional clean the system once a year.

If you’re looking for an HVAC company that serves Tulsa, OK, we can help with inspection, cleaning, maintenance, and even replacement of your HVAC system. Feel free to contact us for questions, consultations, or appointments.

Cody Dampf

Owner

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