What is a Defrost Cycle?

What Is a Defrost Cycle on a Heat Pump?

If you’ve ever noticed your heat pump making strange noises on a cold day—or even sounding like a “jet taking off”—you may have witnessed the defrost cycle in action.

The defrost cycle is a normal and essential process that keeps frost and ice from building up on your outdoor heat pump coils during freezing weather in the Tri-Cities. Without it, your system would lose efficiency, waste energy, and eventually suffer serious damage.

How the Defrost Cycle Works

The simple explanation: The defrost cycle melts ice off your heat pump’s outdoor coils so the unit can keep running efficiently and safely.

The technical explanation:

  • During heating mode, your heat pump pulls heat from outdoor air and transfers it indoors.
  • When temperatures dip near freezing (30°F–20°F), moisture in the air can freeze on the coils.
  • To prevent frost buildup, the unit automatically switches into defrost mode.

Most heat pumps are equipped with a timer or sensor system that triggers defrost cycles every 30, 60, or 90 minutes—depending on your unit and outdoor conditions.

How to Tell if Your Heat Pump Is in Defrost

You’ll know your system is defrosting properly if:

  • There’s little to no frost or ice buildup on the outdoor coils
  • The indoor fan stops temporarily
  • The outdoor fan also pauses
  • You still hear the outdoor compressor running (often louder than usual)

Some customers describe the noise as a “jet engine” or even a “dying moose.” Believe it or not—that’s completely normal during defrost.

When to Call for Heat Pump Service

If your heat pump is defrosting too often, not enough, or not at all, frost and ice can accumulate and cause damage. Common warning signs include:

  • Ice buildup that doesn’t melt away
  • The system struggling to heat your home
  • Defrost cycles that seem unusually frequent or irregular

In these cases, it’s best to have your system inspected by a professional.

At Jacobs and Rhodes, we provide 24/7 emergency HVAC service in Kennewick, Pasco, and Richland, so you’re never left in the cold.

Learn More from Jacobs and Rhodes

Want to see the defrost cycle in action? Check out our YouTube video for a walkthrough—and let us know what other HVAC tips you’d like to learn about.

📞 Call Jacobs and Rhodes today for expert heat pump service in the Tri-Cities. We’ll make sure your system is running efficiently all winter long.