As an HVAC technician, your job doesn’t end with the HVAC system installation; maintenance and troubleshooting are a big part of the routine. A common issue you might encounter during the winter months is a heat pump freezing up on your client. This guide from GREE will walk you through the causes of a frozen heat pump and how to fix it, ensuring optimal performance and client satisfaction.

How Do Heat Pumps Work?

A heat pump transfers heat from one place to another. During winter, it extracts heat from the outside air (even when it's cold, there's still heat in the air) and moves it inside to warm the home. This process is facilitated by refrigerant, a substance with a very low freezing point that can absorb and release heat as it circulates through the heat pump.

The Heat Pump Refrigerant Process:

Here's how refrigerant moves through a heat pump system:

1. During the heating cycle, the heat pump's outdoor unit has a coil that acts as an evaporator. The refrigerant inside the heat pump lowers the temperature of the coil below the ambient outdoor temperature, causing the coil to absorb heat from the outdoor air. The absorbed heat causes the low temperature liquid refrigerant to change state to a warmer vapor.
2. This vapor is then compressed by the heat pump's compressor. Compressing the gas increases its pressure, causing it to become hot.
3. The hot refrigerant vapor then moves to the indoor unit's coil, where it releases its heat into the home. As the refrigerant releases heat into the home, it cools and condenses back into a liquid.
4. The refrigerant, now a cool liquid again, returns to the outdoor unit to repeat the cycle.

Understanding the Causes of a Heat Pump Freezing in Winter

When the heat pump is extracting heat from the outdoor air, the outdoor coil's surface temperature can get very cold. Any moisture in the air that meets the coil can condense and freeze on the coil's surface.

The freezing of condensate is more common in colder climates or during particularly cold periods. This is why heat pumps have a defrost cycle to periodically melt any frost or ice that builds up on the outdoor unit. However, the right circumstances can build on each other to stop the defrost cycle from working properly and lead to heat pumps freezing up in the winter.

Here are some additional items that can lead to a heat pump freezing in the winter.

1. A malfunctioned defrost cycle: As previously mentioned, the defrost cycle keeps the air conditioner warm and prevents heat pump freeze-up. If the defrost cycle is malfunctioning in a cold environment, it can easily be the culprit behind a frozen heat pump. There are a multitude of things that can cause it to malfunction including low refrigerant, a faulty thermostat, incorrect thermostat settings, and extremely humid and cold winter conditions.
2. Extreme weather and temperatures: In addition to extreme cold potentially being the cause of defrost cycle malfunctions, if a heat pump gets covered in snow and freezing rain from extreme weather conditions it certainly won’t help and can exacerbate any issues going on inside the heat pump. Make sure the heat pump is installed above the snow line, and in a place where water will not drip onto it. If conditions outside are too extreme for the heat pump to bear, attempts to kick the unit into defrost mode may fail, or the unit may struggle to melt the ice. It’s important to help your client select a heat pump mini-split system that is suitable for their outdoor environment, GREE is proud to offer the Multi+ Ultra for contractors & their clients in extreme outdoor climates.
3. Restricted airflow: When the airflow inside the heat pump is constricted, the heat pump may not be able to extract enough heat to keep the air conditioner warm. The most common cause of restricted airflow is blocked filters, which can occur due to lack inconsistent maintenance or debris entering the heat pump and blocking the air vents. Another common cause of restricted airflow are dirty outdoor and indoor coils. If using a ducted heat pump, ensure the ductwork is sized properly to provide enough air flow.
4. Miscellaneous Technical Malfunctions Leading to Frozen Heat Pumps: The defrost cycle isn’t the only component of the heat pump that can lead to a freeze up. The heat pump consists of multiple complex components with moving parts, which can malfunction and can hinder the defrost cycle. Damaged or poorly functioning fan motors can reduce the amount of heat inside the heat pump, resulting in icing. If the reversing valve is stuck, this can also cause the heat pump to malfunction and lead to a freeze up.

Fixing a Frozen Heat Pump:

While the exact steps to fixing a frozen heat pump will depend on the multitude of things that could be going wrong with it, here is a list of items you can address that can cause a heat pump to freeze up. Be sure to sign your team up for a GREE group training session so that you’re all familiar with troubleshooting and fixing GREE products!

1. Clear the Area Around the Outdoor Unit: Obstructions like snow and ice can hinder your outdoor heat pump unit, impeding essential heat transfer and potentially causing your heat pump to freeze during winter. It's crucial to evaluate if the environment is affecting the heat pump's capacity to draw in outdoor air. Ensure you maintain a clear space around your outdoor heat pump unit.
2. Check and Adjust Thermostat Settings, or Replace It: If the heat pump is freezing, it could be because the defrost cycle isn't functioning as it should be. Possible causes could be a malfunctioning thermostat or improper thermostat settings. To resolve this, check and adjust the thermostat settings or replace the thermostat if necessary.
3. Refrigerant levels: If the refrigerant levels in the heat pump are low, it can lead to freezing. The refrigerant facilitates the movement of heat from the condenser to the indoor air handler. When levels are low, the heat pump might struggle to bring enough heat into the house. If the refrigerant is low, find and fix any leaks that may exist, then refill it to the appropriate level.
4. Blower motor and fan blades: The failure of the blower motor or dirty fan blades can also contribute to the heat pump freezing. Signs of a faulty blower motor can include the fan starting and stopping intermittently or running at a slower speed. Dirty fan blades can affect the unit's airflow and potentially trap moisture inside, leading to freezing. Make sure to clean the fan blades and replace the blower motor if it's not working properly.
5. Blockages: If there are blockages in the drains inside the unit or in the airflow, it can result in freezing. Blocked drains can accumulate moisture, which can freeze. Restricted airflow, possibly due to blocked filters or air vents, can prevent the heat pump from extracting enough heat to stay warm. Regular checks and cleaning can help prevent these issues from arising.
6. Reversing valve: The reversing valve in a heat pump switches the system between heating and cooling modes. If this valve is stuck, it can lead to inadequate airflow and potentially cause freezing. If the reversing valve is the issue, it might need to be replaced.
7. Dirty coils or filters: Low airflow caused by dirty filters or coils hinder the system’s ability to absorb and release heat. Clean or replace dirty filters. If it is necessary to clean the outdoor or indoor coil, use a gentle cleaner that does not use acid or alkaline substances as those can damage protective coatings on the coil.

Preventing a Heat Pump from Freezing in the Future

No one wants to experience a frozen heat pump, especially in the dead of winter. Here are some steps that you can take with your clients to minimize the chance of it a heat pump freezing in the winter.

1. Select a Heat Pump System rated for Cold Climates:

   As HVAC professionals, you know how crucial it is for a heat pump to operate efficiently during freezing temperatures. Working overtime to compensate for the chilly conditions, some heat pumps might face a dip in performance. Some units might even require supplementary heat sources in emergencies. Hence, it's important to recommend a heat pump with an excellent cold climate performance rating to your clients.

   Here at GREE, we have developed the Multi+ Ultra, a resilient multi-zone mini-split heat pump system, ideal for even the harshest climates. This system features a unique-to-GREE 2 stage / 3 cylinder variable speed compressor, ensuring optimal comfort at temperatures as low as -31F and as high as 115F. With features like the corrosion-resistant, acrylic resin coil coating, it maintains top energy efficiency irrespective of how cold it gets.

   Equip your clients with the best in the market, and ensure their comfort all year round. Don't forget, as GREE contractors, you can use our System Builder App to create custom HVAC solutions for your clients!

2. Proper Installation: Contractors play a critical role in ensuring the proper installation of heat pumps to prevent winter freeze-ups. A well-installed heat pump is critical for efficient operation, extended unit life, and reliable performance during the cold season. The outdoor unit should be installed on a level concrete base, with a minimum clearance of two feet around the unit to facilitate optimal airflow and heat absorption. Strategic placement can also prevent the unit from being inadvertently covered in snow from plowing in the winter. Another critical consideration during installation is the setup of multi-zone systems. Contractors must ensure that the runs between indoor and outdoor units aren't so long that they impede heat transfer. This can be a common issue in multi-zone systems and addressing it during installation can help prevent potential freeze-ups. Proper installation of a heat pump is a cornerstone in preventing winter freeze-ups and ensuring year-round functionality.
3. Regular Maintenance: Schedule HVAC services at least twice a year with your clients, preferably in the fall and spring when the temperatures are milder and the load on the unit will be less. This regular check-up can help identify potential problems and fix them before they lead to a frozen unit.
4. Air Filter Replacement: Encourage your clients to clean or replace the air filter every 30-60 days. A clogged air filter can cause the heat pump to use more energy to pump air, increasing energy costs and potentially leading to a freeze-up under winter conditions.

As contractors, it is essential to have a comprehensive understanding of how to fix and prevent heat pumps from freezing in the winter. Proper heat pump unit selection, installation, and maintenance can all play a substantial role in helping to avoid heat pump freeze ups. As a contractor, you can rely on GREE's mini-split heat pumps, which combine efficiency and flexibility, along with their readily available replacement parts, to keep your clients' HVAC systems running optimally year-round. For additional guidance, GREE offers instructional videos and an FAQ page, providing valuable resources for your installation projects. With your expertise and GREE's reliable solutions, you can deliver the ultimate climate control experience to your clients' homes and businesses.