What Causes a Heat Pump to Freeze Up?
A heat pump freezing up in winter is a stressful experience, not only because it means your heat pump needs servicing, but also because you no longer have heat. A heat pump doesn’t generate heat. Instead, it transfers heat from outside to inside or vice versa. A frozen heat pump can no longer do its job effectively, though. Below are some reasons your heat pump is freezing up outside.
How a Heat Pump Works in Winter
Before understanding what causes a heat pump freezing up outside, it’s important to know how heat pumps work. Heat pumps extract heat from the outdoor air or the ground and transfer it indoors. Even when temperatures are freezing outside, heat pumps can still absorb heat from the air.
The refrigerant in the heat pump’s outdoor coil absorbs the outdoor air, compresses it, and turns it into a gas. Next, the heat pump’s indoor coil condenses the heated gas into liquid and distributes it throughout your home.
During this process, the outdoor coil often becomes colder than the surrounding air. When moisture from the surrounding air comes in contact with the coils, the moisture freezes, resulting in a thin layer of frost. This thin layer is normal. Heat pumps are designed to have an automatic defrost mode, which periodically melts this layer.
What’s Causing Your Heat Pump to Freeze
While a thin layer of frost on your outdoor unit is normal, a thick layer isn’t. Here are some reasons your heat pump is freezing up.
Limited Airflow Around Your Outdoor Unit
Limited airflow around your outdoor unit prevents it from absorbing and dissipating heat effectively. High levels of snow can physically block the exchange of air, while vegetation or stored items within two feet of the unit can block airflow as well. Furthermore, if your outdoor unit is within an enclosed space, it may be sucking back the cold air it’s discharging.
Dirty or Damaged Outdoor Coils
If there’s a thick layer of dirt on your outdoor coils, it can act as an insulating layer, preventing the unit from absorbing heat. The temperatures of the outdoor coils then drop below freezing, creating a layer of ice.
Bent fins also limit how the heat pump absorbs heat, as they prevent a healthy airflow in and out of the unit. In addition, if your outdoor coils are corroded, their ability to transfer heat is significantly reduced.
Refrigerant Levels Are Low
Low refrigerant levels are another reason your heat pump is freezing up outside. Low refrigerant causes the pressure in the outer coils to drop. This pressure drop then results in the remaining refrigerant expanding, lowering the temperatures of the coils, often below freezing. However, it’s important to note that refrigerant circulates in a closed loop within the unit. If your refrigerant levels are low, there’s a leak in the system.
Problems With Your Defrost Cycle
Your heat pump’s auto defrost mode works by sending hot refrigerant to the outdoor coils to warm them up and melt the thin layer of frost. If the defrost cycles are too infrequent, the heat pump can’t effectively remove this layer, causing it to build up and harden. Alternatively, the defrost cycle may be too short, so there isn’t enough time to fully melt the frost layer. Lastly, a faulty sensor may not activate the defrost cycle, causing ice and frost to continuously accumulate on the heat pump.
Drainage Problems
If your heat pump’s base pan heater isn’t working, melted ice can refreeze again. The base pan heater is a small electric heating element that you’ll find at the bottom of your outdoor unit. If your winters are mild, your base pan heater may not be necessary. However, as temperatures drop below 32 degrees Fahrenheit, a base pan heater can ensure melted ice running off your outdoor coil doesn’t freeze.
Wrong Size Heat Pump
A heat pump that’s too small for your home will be forced to run constantly. This continuous attempt to reach your desired temperature leaves no time for the auto defrost cycle to activate, resulting in a buildup of ice.
Lack of Regular Maintenance
Unfortunately, a lack of regular maintenance can also be the reason your heat pump’s outer unit is freezing up. If you miss an annual inspection, professional technicians can’t catch small issues. These small issues may escalate, resulting in major repair concerns.
Maintenance technicians can also identify air filter and airflow problems, allowing you to address them early before they affect your outdoor coils. Technicians can replace overworked and worn-out components as well, so that they don’t cause mechanical issues.
Maintenance tasks that reduce the risk of your heat pump freezing include:
- Cleaning fan blades and dirty outdoor coils
- Ensuring there are no airflow problems
- Making sure air filters aren’t clogged
- Checking the refrigerant levels
- Inspecting all components to ensure they’re working efficiently
What You Shouldn’t Do When a Heat Pump Freezes
If your heat pump’s outdoor unit freezes, contact our Birmingham One Hour technicians immediately. While you wait for our team to arrive, here’s what you shouldn’t do:
- Don’t chip the ice from the coils: Coils are fragile and can easily be bent or flattened. Worse, if you use sharp tools like an ice pick, it can puncture the refrigerant lines beneath the ice.
- Don’t pour hot water on the coils: Pouring hot water on freezing coils can cause small cracks. And if the hot water doesn’t drain immediately, it can quickly refreeze, causing an even thicker layer to form over the outdoor unit.
- Don’t run the heat pump: Having a frozen outdoor unit means you have a major repair issue on your hands. Turn it off and contact our team. We respond fast, especially for emergencies like these. In fact, we’re on time or you don’t pay a dime.
Signs Your Heat Pump Is Frozen
Not sure if your heat pump’s outdoor unit is freezing up? Here are some signs to look for.
- Thick layer of ice: The outdoor coil will have a thick layer of ice, not just a thin layer of frost.
- Cold air: Although your outdoor fan will be running, you’ll feel little to no heat indoors.
- Unusual noises: As ice interferes with the outdoor unit’s moving parts, you’ll hear grinding or rattling noises.
- Auxiliary heat mode is on: Your heat pump will switch to the emergency heat mode or the auxiliary heat mode to try to heat your home.
- Frozen water at base of the unit: You’ll notice water freezing at the base of the heat pump’s outdoor unit.
Our Birmingham One Hour Technicians
Reach out to our team of professional technicians in Birmingham, AL, when your heat pump freezes up. We’ll do a comprehensive inspection of everything and let you know what repairs are necessary. Once you approve the repairs, we can get started right away. Our goal is to keep your home warm all year. Contact our team today for help! Remember, we’re on time or you don’t pay a dime.
