How Does a Heat Pump Defrost Cycle Work?

Heat pumps are indispensable to many households, providing efficient heating in winter and cooling in summer. This versatility comes from its ability to transfer heat energy: extracting it from the outdoor air to warm your home during cold months, and removing indoor heat to cool it when it's hot. However, during chilly weather, frost can accumulate on the outdoor coil, potentially impairing efficiency and leading to damage.

Enter the defrost cycle: a crucial function designed to maintain your heat pump's efficiency without wasting energy. If a heat pump cannot effectively defrost, it may suffer from issues like refrigerant leaks or damaged coils, leading to costly repairs.

In this post, we’ll explore the essentials of how your heat pump keeps itself free from ice without compromising performance, covering:

A heat pump's defrost cycle is activated when you turn the unit to its heat setting. Once the heating cycle begins, thermal energy is pulled from the cold outdoor air. This elimination of heat energy causes the temperature in that outdoor area to drop. If the outdoor coil has accumulated enough moisture, this sudden drop in temperature can cause frost to form on the coil.

The resulting frost makes it difficult for the heat pump to draw heat from the air. As a result, it will need to melt away the excess frost to continue warming up your home. This is where the defrost cycle comes in. During this stage, the heat pump will switch to cooling mode to force warm air through the outdoor coil. This process will continue until the outdoor coil temperature reaches 57 degrees.

Without the defrost control board, your heat pump cannot begin a defrost cycle. When the outside temperature reaches 32 degrees, the control board initiates the defrost cycle. Traditional control boards rely on a timer to regulate the temperature. They do this by following timed intervals of 30, 60, and 90 minutes. Alternatively, newer and more energy-efficient boards automatically regulate the temperature by using the temperature reading as a guide. This ability to self-correct helps save a significant amount of energy.

The defrost control board contains sensors that detect changes in temperature. When they pick up on a temperature drop that's big enough to warrant a defrost cycle, the sensors initiate the cycle. To ensure that your heat pump's frost sensors are working properly, it's important to test them on a regular basis. While set on cooling mode, the sensors should read zero (closed). On heating mode, they should say infinite (open). If you see anything other than these settings, reach out to a technician to identify the issue.

As a way to melt the frost from the outdoor coil, heat pumps activate the reverse cycle defrost mechanism. As the name suggests, this method involves switching from the unit's current cycle to the opposite one. For example, if your heat pump is currently set to heating mode, it will automatically switch to cooling mode to force warm air through the outdoor coil. This reverse cycle method allows the coil to defrost fully before the heat pump resumes doing its job.

Various issues can prevent your heat pump from working properly. Some of the most common problems that homeowners face include:

• Refrigerant leaks
• Lack of warm or cool air
• Short cycling
• Blocked outdoor unit
• Unpleasant odors
• Failure to switch modes
• Constant running

It's crucial to schedule regular maintenance to keep your heat pump running smoothly. Our Peak Performance Tune-Up is designed to keep your unit working at optimal performance year-round.