What causes a heat pump to freeze up?

When winter comes, people often use heat pumps to heat their homes. Low outside temperatures can cause your heat pump to freeze, preventing it from functioning properly.


If your heat pump lacks defrost capabilities, there are several factors to consider:


Airflow obstruction: Ice can block airflow, preventing air from flowing smoothly through the evaporator. This may disrupt the normal operation of the system and may cause the system to stop functioning to prevent further damage. Examples of poor airflow include a failed outdoor fan motor or clogged outdoor evaporator coil or fan blades.

Low refrigerant level: A low refrigerant level indicates a refrigerant leak. Without a sufficient amount of refrigerant in the system, the heat pump cannot absorb as much heat. Therefore, if the outside temperature is below 32 degrees Fahrenheit, the coil may freeze.

Faulty reversing valve: Every heat pump system has a reversing valve that changes the direction of refrigerant flow, allowing the heat pump to switch between heating and cooling modes. If the reversing valve fails, the heat pump system may not defrost properly when ice begins to form.

Increased system load: Ice acts as an insulating layer on the evaporator surface, requiring the system to consume more energy to complete the same amount of work. This increased load may cause the heat pump system to operate beyond its design capabilities, resulting in higher energy consumption.

Defrost problem: Ice on the evaporator surface will hinder the evaporation of the refrigerant and the air circulation in the heat pump. The heat pump compressor automatically shuts down to prevent equipment damage. If the heat pump is operated for an extended period of time in cold conditions and a large amount of ice builds up on the evaporator, defrosting may become difficult or impossible. In this case, the heat pump may stop functioning or be damaged by freezing.


If your heat pump lacks defrost functionality, prioritize checking for problems with the defrost control system.


To determine if the defrost control system is malfunctioning, consider the following factors:

Observe the defrost process: Observe the performance of the heat pump during the defrost process. The defrost process should be periodic and last for a specific period of time before stopping. If the defrost process is abnormal, such as the defrost time is too long or defrost is started frequently, there may be a problem with the defrost control system.

Check the defrost sensor: The defrost sensor detects the frost thickness on the evaporator surface to trigger the defrost process. If the defrost sensor fails, it may not be able to accurately detect frost thickness, affecting the normal operation of the defrost control system. Check the defrost sensor for damage or a tight connection.

Check the evaporator: Observe whether there is frost, ice or other abnormal conditions on the surface of the heat pump evaporator. If there is a large amount of frost accumulation, it may be a sign that the defrost control system is not working properly.

Check Controller Settings: Check the defrost parameter settings on the heat pump controller to make sure they are configured correctly. Correct defrost parameter settings are critical to the normal operation of the defrost control system. If the defrost parameters are set improperly, such as the defrost time is too short or the defrost temperature is too low, the defrost control system may not work properly.

Seek professional help: If the above methods cannot determine whether the defrost control system is faulty, it is recommended to contact a professional heat pump technician for inspection and repair. They have the expertise and experience to accurately diagnose any problems with your defrost control system and make the necessary repairs.

Dealing with Heat Pump Frost Problems:


Manual defrost: If the heat pump defrost system is malfunctioning, try manual defrost. Move the defrost sensor to the icy area to trigger the defrost process, helping to loosen and remove frost.

Check sensors and controllers: Check that the defrost sensor and controller are functioning properly. If these components fail or are configured incorrectly, the normal operation of the defrost system may be affected. Repair or replace failed sensors and controls.

Raise the indoor temperature: Raising the indoor temperature can reduce the chance of your heat pump freezing. Use additional heating equipment or increase indoor heating to minimize the risk of frost.

Clean the evaporator: Clean your heat pump’s evaporator regularly to reduce frost buildup. Frost build-up can reduce the efficiency of a heat pump, and regular cleaning can help maintain efficient heat exchange.

Get professional help: If the above measures don’t resolve your heat pump frost problem, consult a professional heat pump technician for a thorough inspection and maintenance. Their expertise and experience allow them to accurately identify the root cause of the problem and make the necessary repairs.


Post time: Dec-23-2023