.ctl-bullets-container { display: block; position: fixed; right: 0; height: 100%; z-index: 1049; font-weight: normal; height: 70vh; overflow-x: hidden; overflow-y: auto; margin: 15vh auto; }
Skip to content

Locating and Inspecting the Defrost Sensor in a Heat Pump

Heat pumps are energy-saving machines that can be used in any home to provide heating and cooling. However, in colder climates, they can become less efficient due to the formation of ice on the external coils. To prevent this situation, heat pumps must enter a defrost mode to clear the ice. In this article, we will tell you where to find the defrost sensor of a heat pump and how to test it if your unit is not functioning properly.


The defrost sensor is a component of the heat pump system that detects ice or frost on the machine’s outdoor coils and triggers the appropriate program to correct the situation. Heat pumps transfer heat from the outside air to the indoors during colder months, helping to improve the environment inside the house. However, if the outdoor coils are covered with ice or frost, they cannot absorb heat properly, resulting in reduced efficiency and potential damage to the system.


How does the heat pump defrost sensor work?

The defrost sensor works by tracking the temperature of the outdoor coils. It typically consists of a timer and a temperature sensor. Once the temperature sensor detects that the outdoor coils have reached a specific temperature, usually around 32 degrees Fahrenheit, the timer is triggered, starting the defrost cycle.


During the defrost stage, the heat pump simply changes the refrigerant flow, warming up the outdoor coils and melting any accumulated ice or frost. This cycle typically lasts a few minutes, and then the heat pump returns to the heating cycle.


The defrost sensor is an important component of the heat pump unit as it helps ensure that the system operates reliably and efficiently even in freezing conditions. A heat pump with a malfunctioning or missing defrost sensor may struggle to meet the demands of cold conditions or experience reduced performance and increased wear and tear.


Some modern heat pumps even use intelligent defrost sensors that take into account humidity and external temperature to enhance the defrost cycle and improve efficiency. These defrost sensors may utilize more advanced algorithms to determine when and for how long the defrost cycle should remain active.


Air sour heat pump cost

Where is the heat pump defrost sensor located?

The defrost sensor is typically located on the outdoor coils of the heat pump, near the outdoor fan motor, where frost or ice is likely to accumulate during cold seasons. It is usually housed within a plastic casing and consists of a timer and temperature sensor.


The sensor is a metal tube or rod that is connected to the heat pump’s defrost control board. It may be visible or have a protective cover. When the outdoor coils reach the specified temperature, the sensor triggers the defrost control board, initiating the defrost cycle.


Knowing the location of the defrost sensor is crucial so that you can regularly check for any signs of malfunction or damage and ensure that your system operates effectively during the cold season.


Some heat pumps may have multiple defrost sensors placed at different locations on the outdoor coils to ensure precise detection of ice deposition. The exact positioning of the sensors may vary depending on the heat pump model and manufacturer. If you need assistance in locating the defrost sensor on your heat pump unit, refer to the user manual or contact the manufacturer for help.


To defrost the heat pump, the defrost control must accomplish four things:

  • Switch the reversing valve from heating to cooling.
  • Turn off the outdoor fan.
  • Activate the auxiliary heat source.
  • Provide power to the indoor blower motor.


The most common method to determine when defrosting should start is based on time and temperature. A defrost sensor is installed on the outdoor unit’s coil and is used in conjunction with a timer to accumulate the heat pump’s running time. The defrost sensor must be closed. When the outdoor coil temperature drops low enough to frost or ice over, the sensor closes. Once closed, the defrost control board begins to accumulate the running time of the compressor.


Defrost troubleshooting:

Since the defrost sensor plays a crucial role in the operation of the heat pump during heating mode, here are some symptoms that may indicate a faulty defrost sensor.


A heat pump with a faulty defrost sensor may exhibit the following symptoms:

  • Ice formation on the outdoor coil.
  • The outdoor fan may run continuously or intermittently.
  • The heat pump may take longer than usual to defrost.
  • The heat pump may fail to reach the desired temperature.
  • The outdoor unit may produce loud noises during operation.
  • The heat pump may cycle on and off frequently.
  • The heat pump runs continuously without providing any heat.

Looking for heat pump provider?

Shenling will be the best solution of how to use a heat pump in winter

What are the signs of a faulty heat pump defrost sensor?

If the defrost sensor of your heat pump is faulty, you may observe several signs, including:

  • Formation of ice on the outdoor coils
  • Continuous or frequent running of the outdoor fan
  • Longer defrost cycles than usual
  • Inability to reach the desired temperature
  • Loud noise coming from the outdoor unit
  • Frequent cycling on and off
  • Continuous operation but no heat being generated
  • Checking the heat pump defrost sensor

Once you have identified the defrost sensor of your heat pump, you can proceed to check it to ensure it is functioning correctly. There are several methods to check the defrost sensor.


Continuing from where we left off:

One method is to check for continuity. First, use a multimeter to test for continuity, which means checking if the defrost sensor’s circuit is complete when it is closed. To do this, turn off the power to the heat pump and remove the electrical cover of the outdoor unit.


Once you locate the defrost sensor, use the multimeter to verify its continuity. If you do not detect continuity, the sensor is likely faulty and needs replacement.


Another method is to measure the temperature of the outdoor coils. You can use a special temperature probe to measure the temperature of the heat pump’s outdoor coils and determine if the defrost sensor is working correctly. Find the outdoor unit of the heat pump, open the service panel, and you should see the coils. Power on the heat pump for at least 10 minutes to allow it to reach a stable temperature.


Place the temperature probe on the surface of the coils for temperature readings. Take multiple readings across the coil to ensure a reliable average temperature estimate.


If the defrost sensor is functioning correctly, it should trigger the defrost cycle when the coils reach the specified temperature, and you should see the ice or frost melting away.


It is essential to perform regular checks on the defrost sensor, especially before the onset of colder months, to ensure it is in good working condition. If you notice any signs of malfunction or inefficiency, it is best to have a professional technician inspect and service your heat pump to ensure optimal performance and energy efficiency.


In conclusion, the defrost sensor is a crucial component of a heat pump system, ensuring its efficient operation even in freezing conditions. By understanding its function, location, and signs of failure, homeowners can take proactive measures to maintain their heat pump and enjoy comfortable indoor temperatures throughout the year. If you are unsure about any aspect of your heat pump’s defrost sensor or need assistance, always consult a qualified HVAC technician for proper diagnosis and repair.

Related posts

Related heat pump products

Get Quote