Why is My Heat Pump Freezing Up in Winter (Causes, Prevention, and Solutions)

Figure 1: Heat pump units.

A heat pump is an essential component of any HVAC system, providing both heating and cooling functions. However, during the winter months, it's not uncommon for homeowners to experience issues with their heat pumps freezing up. This can be a frustrating and potentially costly problem, as it can lead to reduced efficiency, increased energy bills, and even damage to the system.

In this article, we'll explore the reasons why a heat pump may freeze up in winter (heat pump freezing up in heat mode) and what you can do to prevent and fix the issue.

1. Understanding How Heat Pumps Work

Before we dive into the causes of heat pump freezing, let's take a moment to understand how they work.

Heat pumps work by transferring heat energy from one place to another relaying on the compressor, evaporator, condenser, expansion valve, etc. During the winter months, they extract heat from the outside air and transfer it into your home to provide warmth.
However, when temperatures drop below freezing, moisture in the air can freeze on the outdoor unit's heat exchanger, causing ice buildup.

This ice can impede airflow and reduce the heat pump's efficiency, which can cause it to work harder and use more energy to provide the same amount of heat. Additionally, if the heat pump is low on refrigerant or the defrost cycle malfunctions, ice buildup can occur more frequently.

Figure 2: Heating principle diagram of water source heat pump unit.

2. Causes of Heat Pump Freezing up in Winter

There are several reasons why a heat pump may freeze up in winter. Here are some of the most common causes:

2.1 Low Refrigerant Levels

Refrigerant is the substance that flows through the heat pump's coils, absorbing and releasing heat energy. If the refrigerant levels are low, it can cause the heat pump to operate inefficiently, which can lead to ice buildup on the outdoor unit.

2.2 Dirty Air Filters

Air filters are responsible for removing dust, dirt, and other contaminants from the air before it enters the heat pump. If the air filters are dirty, it can restrict airflow, which can cause the heat pump to work harder and lead to ice buildup.

2.3 Malfunctioning Defrost Cycle

The defrost cycle is responsible for melting any ice that accumulates on the outdoor unit's heat exchanger. If the defrost cycle malfunctions, it can cause ice to build up on the unit, which can impede airflow and reduce the heat pump's efficiency.

2.4 Extremely Cold Temperatures

When temperatures drop too low, moisture in the air can freeze on the outdoor unit's heat exchanger, causing ice buildup. In areas with cold climates, it may be necessary to install a supplemental heat source, such as electric heating strips, to provide additional warmth during extremely cold weather.

Figure 3: Mitsubishi air source heat pump.

3. Preventing Heat Pump Freezing up in Winter

Now that we've explored the causes of heat pump freezing in winter, let's take a look at some preventative measures you can take to avoid the issue.

3.1 Schedule Regular Maintenance

Regular maintenance and inspections performed by a qualified HVAC technician can help prevent heat pump freezing. They can check the refrigerant levels, ensure the defrost cycle is functioning properly, and clean the outdoor unit to remove any debris that can obstruct airflow.

3.2 Clean Air Filters

Cleaning the air filters regularly can help ensure proper airflow and prevent ice buildup on the heat pump.

3.3 Install a Freeze Sensor

Installing a freeze sensor is another effective way to prevent your heat pump from freezing up. These sensors are designed to detect when the outdoor temperature drops too low, automatically activating the defrost cycle. By doing so, they help prevent ice buildup on the coil, ensuring that the system continues to operate efficiently.

Figure 4: Temperature sensor for heat pump.

3.4 Keep Your Coils Clean

Keeping your coils clean is critical to ensuring that your heat pump operates efficiently. Over time, dirt and debris can accumulate on the coils, reducing their ability to transfer heat. By cleaning the coils regularly, you'll ensure that they can absorb heat from the outdoor air effectively, preventing the evaporator coil from becoming too cold.

3.5 Install a Programmable Thermostat

A programmable thermostat can help regulate the temperature in your home more efficiently, which can reduce the amount of time your heat pump needs to run and prevent ice buildup.

3.6 Use a Heat Pump Cover

A heat pump cover can help protect the outdoor unit from the elements, reducing the risk of ice buildup. However, it's important to use a cover specifically designed for heat pumps, as using an improper cover can impede airflow and cause more harm than good.

4. How to Fix a Frozen Heat Pump

If your heat pump has already frozen up, here are some steps you can take to fix the issue:

4.1 Turn Off the Heat Pump

Turn off the heat pump to prevent further damage. Allow the ice to melt naturally or use a hairdryer on the low setting to speed up the process.

Figure 5: air source heat pump water heater control board.

4.2 Check the Air Filters

Check the air filters and replace them if they're dirty. This can help ensure proper airflow and prevent ice buildup in the future.

4.3 Check the Refrigerant Levels

Have a qualified HVAC technician check the refrigerant levels and add more if necessary. Low refrigerant levels can cause the heat pump to operate inefficiently, leading to ice buildup.

4.4 Check the Defrost Cycle

Have a qualified HVAC technician check the defrost cycle and repair or replace any malfunctioning components. A properly functioning defrost cycle is critical to preventing ice buildup on the heat pump.

5. Conclusion

Heat pump freezing in winter can be a frustrating and potentially costly problem. However, with proper maintenance and preventative measures, you can avoid the issue and keep your heat pump running smoothly.

If your heat pump does freeze up, taking the proper steps to fix the issue can help prevent further damage and ensure your system operates efficiently for years to come.

Related Info