Understanding Heat Pump Defrosting: How Does a Heat Pump Know When to Defrost?

A heat pump, like a 2014 Goodman model with a single-speed compressor and 14 SEER (Seasonal Energy Efficiency Ratio), uses various methods to determine when to defrost. Defrosting is a critical process that ensures the outdoor coil doesn't become iced over, which can significantly reduce the system's efficiency and performance.

Heat Pump Defrost Mechanisms

Not all heat pumps use the same method for defrosting. Some rely on a simple defrost timer, which is typically set to intervals of 30, 60, or 90 minutes. However, this timer can be modified based on the local climate. For instance, if you live in an area where the nights are predominantly above freezing (30°F), you might set the timer to 90 minutes. In colder climates, you might set it to 45 minutes to address more frequent and severe ice buildup.

Temperature-Sensor-Supported Defrosting

Other types of heat pumps use a temperature sensor on the suction line. This sensor monitors the temperature of the refrigerant leaving the evaporator. When it drops to a certain threshold, such as 12°F, indicating that ice has accumulated on the outdoor coil, the heat pump automatically initiates the defrost cycle. This method is more accurate and less prone to over-defrosting or under-defrosting.

Defrost Termination

Once the defrost cycle starts, there are several conditions that can cause it to terminate. Typically, the process relies on either a set time or a temperature sensor on the liquid line. For example, if the defrost has been running for more than 8 or 10 minutes, as determined by the manufacturer, the defrost cycle will terminate. Alternatively, if the liquid line reaches a specific temperature, such as 38°F, indicating that the ice has melted and the system can resume normal operation, the cycle will also end.

Regional Adjustments

In warmer regions where the outdoor temperature remains consistently above freezing (e.g., 55°F), the defrost termination sensor might already indicate that defrosting is unnecessary. Therefore, if the defrost timer dictates a defrost at 90 minutes, but the liquid line sensor shows a temperature of 38°F or higher, the system will not defrost. Instead, the defrost timer will reset, and the process will wait for the next specified interval.

Conclusion

Understanding how a heat pump knows when to defrost is crucial for maintaining optimal performance and efficiency. Whether relying on a timer or temperature sensors, the system is designed to ensure that the outdoor coil remains clear of ice, improving overall energy efficiency and reducing operational costs. By adjusting the defrost settings based on your local climate, you can optimize your heat pump's performance.