As a Gilbert, AZ resident, you rely heavily on your HVAC system to keep you cool and comfortable during the long, hot summers. Yet, when a chilly winter night arrives, you also rely on your heat pump to keep your home warm and cozy. If you own a heat pump, you may have noticed that during cold, damp periods, the outdoor unit may sometimes have issues with reliable heating. It might produce a puff of steam or even develop a thin layer of frost. You might think your heat pump is failing, but it’s not. It’s actually a sign that your system is operating the way it’s meant to. You’re seeing the defrost mode in action.
All heat pump owners need to understand the heat pump defrost cycle, especially in desert climates like ours. While our winters in Gilbert are mild, the combination of relatively cool temperatures and humidity can lead to frost on the outdoor coil. At A/C & Plumbing Doctors, we want you to know how the defrost function works, why and how it operates, and what you should and shouldn’t do when you notice your heat pump switching into defrost mode.
Why the Defrost Mode Is Necessary
A heat pump extracts heat from the cold outdoor air and transfers it inside your home. The process is highly efficient, but it requires the outdoor coil to be colder than the ambient air to effectively pull heat from it.
When the outdoor temperature drops below the low- to mid-40s Fahrenheit, which are the typical lows between December and February, and there is enough moisture present in the air, the coil’s super-cooled surface acts like a freezer. Any condensation that touches the coil freezes and forms a layer of frost or ice.
Frost acts as an insulator. Even the thinnest layer of ice blocks the coil’s ability to absorb heat from the surrounding air. When this happens, the heat pump can’t heat your home as efficiently.
Airflow becomes restricted, making it difficult for air to pass through the coil fins. This starves the HVAC system of the heat it needs to warm your home. The compressor also becomes stressed during the heat transfer process. You might notice that the unit working harder and longer. You might also notice an increase in energy usage. Any time a component works harder than necessary, it causes the system to overheat and potentially fail prematurely.
Your heat pump’s defrost mode is the smart, automatic solution engineered to combat this specific issue, ensuring your heat pump remains efficient, effective, and in good working order throughout the cooler months.
How Your Heat Pump Automatically Enters Defrost Mode
Today’s heat pumps have a sophisticated circuit board and various sensors to determine when to activate the defrost cycle. The system doesn’t rely on a simple timer. Instead, it monitors actual operating conditions and relies on two triggers.
The pump initiates a defrost cycle based on two main conditions: temperature and runtime. When the temperature sensor detects coil temperatures around 32 degrees Fahrenheit, it kicks on. Also, if the system has been running in heating mode since the last successful defrost cycle and hasn’t kicked off according to the set amount of time, the defrost control board signals the system to reverse its operation. Typical runtimes for a heat pump in the defrost cycle range from 30 to 90 minutes.
The Defrost Cycle: A Temporary Change in Operation
When the heat pump shifts into defrost mode, the pump might shift into reverse mode, which is what happens when the pump momentarily switches from heating mode to cooling mode. In normal heating mode, the heat pump absorbs heat outside and releases it inside. In cooling mode (defrost mode), it temporarily draws hot refrigerant from your home and sends it back to the outdoor coil.
You might also notice the heat pump utilizing residual heat by running in cooling mode. When this happens, the
hot refrigerant bypasses the indoor coil and instead flows into the outdoor coil, rapidly warming it. With this sudden injection of heat, frost melts along with any ice accumulated on the coil fins.
To prevent your home from blasts of cool air while the outdoor unit is heating up, your heat pump system automatically engages the auxiliary or emergency heat strips (electric resistance heat) inside your furnace or air handler. It does this to maintain comfortable indoor temperatures throughout the short defrost period. It is because of this that you might notice your indoor unit continuing to run and warm air coming out of the vents. The outdoor fan will usually turn off to speed up the melting process, though.
Once the frost sensors detect that the outdoor coil is warm enough and the ice has melted (or the maximum defrost time has been reached), the reversing valve switches back to normal heating mode, and the auxiliary heat turns off. The system then resumes its normal energy-efficient process of heating your home.
What to Expect and What Not to Do During Defrost Mode
As a heat pump owner, it’s a good idea to know what normal defrost operation looks like and how to avoid causing damage to your system.
Normal operations:
- Puffs of steam
- Gurgling noises
- Water accumulation on the ground
- Brief indoor air cooling
- Outdoor fan turning off
What to never do to your heat pump:
- Pour hot water on the coil
- Attempt to chip the ice away
- Let snow/debris pile up
If your heat pump seems to be running in defrost mode for more than 20 minutes or is completely covered by a thick layer of ice for hours, contact a professional. You need to address problems head-on to avoid breakdowns and expensive repairs. You’ll appreciate having peace of mind, knowing that your heat pump is primed to work well for your home throughout the year.
Heat Pump Maintenance and Repair
A healthy defrost cycle is a sign of a healthy heat pump. If you have any concerns about your heat pump’s performance, especially during the cold snaps we experience in Gilbert, you can trust our team of experts at A/C & Plumbing Doctors. Understanding heat pump technology is our specialty, and we provide the professional, hands-on care your system needs.
We offer comprehensive heat pump tune-up services to ensure all sensors, valves, and components are functioning optimally before the cold weather hits. Our other essential services include AC repair for the summer months and furnace maintenance for dual-fuel systems. Trust our professional team to keep your home comfortable and energy-efficient year-round.
Contact A/C & Plumbing Doctors today for more information about our heat pump services!
