Why Do Heat Pumps Have Defrost Systems?

by | Feb 7, 2023 | Heating

Key Takeaways

Why heat pumps have defrost systems:
  • Prevent Ice Buildup: Ensures efficient operation in cold weather by melting frost on coils.
  • Maintain Efficiency: Helps heat pumps provide continuous heating without overworking.
  • Automatic Operation: Utilizes sensors and timers for seamless defrost cycles.
Check out InMotion Mechanical’s heat pump repair service.

If you regularly check your heat pump, you may have noticed it goes through a defrost cycle once in a while. For instance, your heat pump will likely defrost in winter or when the temperature drops significantly.  

So, what exactly is a defrost cycle, and why do heat pumps have to defrost?

The defrost cycle helps your heat pump operate more efficiently. How heat pumps operate can be complex for an average homeowner to understand, leading them to believe their heat pump is malfunctioning. 

This guide will unravel the mystery surrounding heat pumps and explain what a defrost cycle is and how it works. Let’s dig in! 

A Basic Rundown on Heat Pumps

A heat pump is an electronic device that can heat a house by transferring heat energy from the outside using a refrigeration cycle. 

Despite what its name implies, a heat pump can provide warm and cool air. 

A heat pump works by extracting heat from the cold air outside into your home. This way, a heat pump can also provide cooling by transferring warm indoor air outside. In other words, it can heat and cool your home. 

What Is a Heat Pump Defrost Cycle?

In heating mode, a heat pump draws heat from the outside air and transfers it into your home. When the outdoor temperatures are extremely low (close to 0 degrees or below), the moisture in the air freezes on the outdoor unit’s heating system, resulting in frost on the system coils. 

The frost build-up ultimately makes the unit work harder and needs to be removed to improve the system’s efficiency. The defrost cycle is what removes the frost. 

How Does the Defrost Cycle Work?

When the temperature drops significantly and there’s ice on the outdoor coil, your heap pump enters defrost mode. 

A particular sensor, called a frost thermostat, located at the bottom of the coil detects its low temperature. The thermostat closes the coil circuit when the temperature falls below 32 degrees F, which triggers the internal timer. 

Many heat pumps have a timer that activates the defrost relays at specific intervals, usually every 30, 60, and 90 minutes. The defrost relays turn on the pump’s reversing valve, switching it to cool mode. The system has now entered the defrost cycle. 

Some models have a visual indicator that tells when the system has entered into the defrost cycle. If your heat pump doesn’t have a visual indicator, you’ll know it’s in defrost mode once it stops blowing hot air. In defrost mode, the heat pump dissipates the heat outside, which warms the outdoor coil, causing the ice to melt. 

How to Tell if the Heat Pump Is Functioning Properly

There are a few things that can indicate you may need heat pump repair services

For instance, if the defrost cycles initiate even when the temperature outside is above average, you may need to have it checked by a professional. A well-functioning heat pump shouldn’t go into defrost mode if the outdoor temperatures exceed 32 degrees C. 

Check also the heat pump defrost time. A functioning heap pump shouldn’t run longer than five to fifteen minutes, the length of a typical defrost cycle. 

Key Takeaway

Heat pumps go into a defrost cycle to operate more efficiently. In defrost mode, the unit dissipates heat on the outdoor coils, which helps melt the ice. If your unit switches to defrost mode in winter, there’s nothing to worry about. 

But if the unit goes into defrost mode frequently, even when the temperatures are above average, you may need to have it checked by an HVAC expert.