What Causes A Heat Pump To Freeze Up

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By Debarghya Roy

Heat pumps are a great way to keep your home warm and reduce energy costs. However, they can have problems if not maintained properly or exposed to extreme temperatures.

In this blog post, we’ll discuss what causes a heat pump to freeze up and how it can be prevented or solved.

Key Takeaways

  • There are several common causes of a frozen heat pump, such as insufficient airflow, technical malfunctions, restricted airflow, excess moisture and low refrigerant levels.
  • Proper insulation in walls and regular air filter replacements can help prevent a frozen heat pump.
  • Signs of an impending problem with your heat pump include strange odors emanating from vents during operation, reduced heating capacity, or unusually loud buzzing noises.
  • To fix any freezing issues that arise it’s important to hire an HVAC technician for diagnosis and repair; they will inspect and clean the filters so proper air circulation occurs again.

How Does Heat Pumps Work?

Heat pumps are HVAC systems that use the heat from outside sources to warm your home. 

They work similarly to an air conditioner, except they run in reverse and transfer heat from the air and ground into your home instead of taking it away.

  • This process works through two sets of coils and evaporator coil located inside and a condenser coil on the exterior. 
  • The refrigerant gas circulates between these two coils, absorbing warmth in one area before moving away and releasing it somewhere else once it’s warmer than its surroundings.
  • A compressor powers this cycle by forcing refrigerant through copper pipes so that it can absorb or release heat energy as needed.

Reasons Why A Heat Pump Freezes Up And Solutions

Insufficient airflow, technical malfunctions, restricted airflow, excess moisture, low refrigerant levels, dirty air filters and a malfunctioning defrost control board are all common reasons why a heat pump can freeze up.

what causes a heat pump to freeze up

Insufficient Airflow

Insufficient airflow is one of the key issues that can cause your heat pump to freeze up. 

When air isn’t properly flowing over and through the coils, temperatures inside may drop down far enough for it to dip below freezing.

As this occurs, ice builds up on outdoor coils causing a frozen heat pump. 

In order to prevent this from happening, make sure all vents are kept clear and unobstructed so the necessary amount of air flow moves freely around your unit.

Technical Malfunction

Technical malfunctions are a common cause of heat pump freezing up. 

Issues such as faulty defrost controls, malfunctioning sensors, and failed components can disrupt the normal refrigeration cycle, causing it to shut off.

If left unfixed, these problems can snowball into further compressor damage due to prolonged exposure to cold temperatures or high humidity in your home’s environment.

It’s important for homeowners to be able to identify warning signs that might indicate an impending technical malfunction with their heat pump unit. 

Signs like,

  • Strange odors emanating from vents during operation could indicate loose wiring connections
  • Reduced heating capacity may mean blockages in air ducts
  • Unusually loud buzzing noises could be indicative of faulty fan motors or bearings coming apart internally.

Restricted Airflow

One of the leading causes of a frozen heat pump is due to restricted airflow, typically as a result from reduced spinning of the fan or improper insulation.

Without sufficient air passing over the coils on an outdoor unit, temperatures can drop below freezing and ice can form on them. 

If air filters are dirty or clogged, it hinders airflow throughout the system which will leave some areas underexposed to adequately heated air that could prevent freezing.

This is why having regular maintenance checks done by professional HVAC technicians is essential in preventing restricted airflow and potential freeze-ups since they can inspect your filters and clean your coils when necessary.

The use of proper quality is much better than standard ones for greater reliability. 

Furthermore, proper insulation also helps reduce frozen heat pumps during winter months because well insulated walls provide added protection against cold weather conditions.

Excess Moisture

Excess moisture is a common cause of heat pump freeze-up. Since heat pumps use refrigerant to absorb and release heat from the air.

Higher levels of humidity can create an unfavorable environment that leads to frost and condensation build up.

If moisture accumulates on the outdoor evaporator coil, it will block airflow from the fan blades or decrease efficiency due to ice entrapment while also preventing pressure equalization on hot days.

Without regular inspection and cleaning inside and out (including air filters) as part of routine maintenance for your heat pump.

Low Refrigerant Levels

It causes a heat pump to freeze up because they reduce the pressure and lower the temperature within the system. 

This in turn affects the ability of the heat pump to transfer heat effectively, as less heat energy is generated by the refrigerant in order to warm or cool air.

Low refrigerant levels can be identified through signs such as reduced heating/cooling capacity, strange noises, unusual odors, etc. 

To solve this issue it is important that users identify any leaks causing low refrigerant levels before topping off their unit with more refrigerant otherwise; they risk damaging their system further.

Dirty Air Filters

Dirty air filters can be the root cause of many heat pump problems, including freezing up. Clogged or old filters restrict airflow, trapping moisture that causes frost to build on the coils and freeze up.

This issue is especially common during hot days when there isn’t enough cold outdoor air to cool off the system’s evaporator and condenser coils. 

Building dust, pet dander, pollen, smoke particles and other debris are regularly trapped by our home air filters.

If left unchanged for extended periods these materials will accumulate in the filter causing decreased airflow.

Servicing your unit with regular cleanings helps remove this buildup and keeps your system running at optimal performance levels.

Malfunctioning Defrost Control Board

A malfunctioning defrost control board can be one of the key factors in a heat pump freezing up over time. 

The defrost control board is an important piece of technology as it measures the amount and rate at which the outdoor coil changes temperature.

It needs to work properly in order for there to be sufficient refrigerant flow, and allow for cool air to reach the indoor evaporator coils, keeping them from accumulating ice or frost build-up.

If this buildup occurs, then it will diminish the heating capacity until eventually leading to a complete freeze-up of your system.

In order to prevent that from occurring, you should look into regularly maintaining and cleaning your equipment including its fan motor.

Inspect its ductwork for any blockages; verify that its refrigerant levels are around normal.

Check if there’s debris on top of the compressor outside unit which affects airflow.

Ensure all outdoor vents located near windows are cleared from snowdrifts or blocked by excess foliage present in winter months.

Other usual suspects like a tank gradually losing water over time due to leaking valves solenoid coils may apply too.

Damaged Fan Blades

One of the main reasons why a heat pump freezes up is damaged fan blades. If these fan blades become damaged due to ice buildup on the outdoor coils.

They are unable to properly circulate air and cause damage to the sensitive fins in the compressor as well as other parts of the system.

When this happens, it can restrict airflow and eventually lead to your heat pump freezing up or losing efficiency resulting in higher energy costs

To prevent this from happening, it’s important that you schedule regular maintenance check-ups for your heat pump including cleaning any dirt and debris off of the fan blades.

Not only will this help ensure proper air circulation but also help reduce wear and tear on other components as well as extend its lifespan by keeping them cool during operation.

Signs Of A Frozen Heat Pump

One of the tell-tale signs of a frozen heat pump is ice on the unit’s exterior and reduced heating capacity.

Ice On Outdoor Unit

Ice accumulation on the outdoor heat pump unit is a common problem in winter months, caused by poor maintenance, insulation or inadequate drainage

During cold weather, excess moisture in the air surrounds the outdoor evaporator coils and when temperatures drop even further it results in condensation forming on these parts, which then freeze into ice.

If there is sufficient snowfall or rain combined with low temperature conditions this process occurs more quickly.

Leading to thick layers of packed ice covering both the inner and outer coils of an outdoor unit.

Reduced Heating Capacity

Reduced heating capacity is one of the most notable indications that a heat pump has frozen up. 

The reduced efficiency in the system usually happens when normal temperatures are outside of its range, such as colder winter months or unusually hot summer days.

Furthermore, inadequate airflow due to build-up on the coils can also lead to insufficient removal of heat from indoors and thereby reducing it’s heating capacity.

Unusual Sounds

Unrecognized or unexplained strange noises coming from your heat pump could indicate various different problems. 

A rapid clicking sound may indicate an electrical issue, while odd banging, screeching, rattling and gurgling sounds can be a sign of mechanical issues inside the system.

Moreover, faint clicking noises suggest bad starter capacitor or compressor motor failure while buzzing and grinding signify too little clearance between fan blades and coil box walls.

If you hear any of these unusual sounds coming from your heat pump, it’s best to call for an experienced technician who can investigate the cause and determine the necessary repairs.

The longer such symptoms are left unrecognized or neglected, the greater chance of severe damage and expensive repair bills becomes.

Strange Odors

Strange odors coming from a heat pump can be very concerning and sometimes mean that there is an underlying problem that needs to be addressed. 

In most cases, these unpleasant smells are caused by something such as a dirty filter, mold or mildew growth, or a refrigerant leak.

These can present potential health hazards for anyone in the home so it’s important to address them promptly.

To identify and address strange odors, start by checking the air filters.

How To Deal With A Frozen Heat Pump?

Turn off the system and let the ice melt, inspect and clean air filters, schedule regular maintenance check-ups, ensure proper airflow around the outdoor unit.

Turn Off The System And Let The Ice Melt

  • Frozen heat pumps can be a major issue during the colder months. 
  • If you notice that your outdoor unit has ice buildup, then it is important to take action as soon as possible by turning off the system and allowing the ice to melt.
  • The reasons for this are significant due to potential risks of operating a frozen heat pump
  • Operating a frozen system could result in water damage, as well as damage to other components such as compressors or evaporator coils if not properly addressed.
  • In addition, low refrigerant levels could further damage your system if they freeze.
  • To prevent any lasting issues and costly repairs, it is best practice to turn off your heat pump and allow all of the ice build up on the outdoor unit to fully melt before returning your system back on again.

Inspect And Clean Air Filters

  • It’s essential to inspect and clean air filters regularly when using a heat pump.
  • Dirty air filters can prevent proper airflow, causing the heat pump to work harder which in turn can cause it to freeze up.
  • Airflow is necessary for a properly functioning heat pump system, so when the filter becomes blocked airflow is inhibited and ice can form on the coils in extreme cases of restriction.

Schedule Regular Maintenance Check-ups

It is important to have your heat pump serviced regularly to prevent it from freezing. 

Maintenance check-ups should be conducted at least once a year, though more frequent service may be required depending on the climate and usage of the system.

During maintenance visits, technicians will inspect and clean all major components such as coils, air filters, indoor/outdoor unit connections, compressor pipes, refrigerant lines, and the condenser fan motor.

They can also advise on potential upgrades or replacements that could increase energy efficiency in years to come. 

Regular maintenance appointments help identify any problems early so they don’t become bigger issues down the road that may result in higher costs for repairs or replacement parts.

Maintenance visits also involve checking venting systems in order to ensure sufficient airflow around the outdoor unit which prevents ice accumulation due to insufficient cooling of refrigerant within coils during winter months.

Ensure Proper Airflow Around The Outdoor Unit

  • Maintaining proper airflow around the outdoor unit of a heat pump is essential in preventing a system freeze-up. 
  • When the outdoor unit receives inadequate air, it has difficulty dissipating heat, causing an over accumulation of ice on its evaporator coil which ultimately leads to a frozen system.
  • This can cause serious damage and lead to expensive repairs.

Prevention Of Heat Pump Freezing

Regular maintenance, timely repairs, proper insulation and ductwork sealing as well as investing in a defrost control board or freeze protection system are the best ways to prevent heat pump freezing.

Regular Maintenance And Cleaning

  • Regular maintenance and cleaning is an essential practice for extending the life of your heat pump, preventing it from freezing up, and ensuring it operates efficiently.
  • Checking air filters regularly to make sure they’re not clogged will help avoid a frozen unit due to restricted airflow. 
  • Parts within the system, such as outdoor coils and evaporator coils should be inspected periodically for dirt build-up that can decrease performance efficiency or cause a freeze-up in colder weather conditions.
  • It is important to also lubricate any moving parts in the system on a regular basis which will reduce friction and extend its lifespan. 
  • Finally, professional maintenance checkups 

Replacing Air Filters Regularly

Air filters are an important part of any air handling system, including heat pumps. 

These parts play a key role in the health and efficiency of a heating system as they filter dirt and other particles that can harm equipment or people’s health.

When these filters become dirty or clogged, it can significantly reduce the airflow which leads to problems like freezing up your heat pump. 

The most common time to have this issue is during cold weather when it’s working more than usual.

Regularly replacing them year-round helps ensure proper airflow within the unit and prevents issues from occurring in both winter and summer months.

Proper Insulation And Ductwork Sealing

Ensuring that a heat pump has proper insulation and sealing is critical to helping protect it against freezing up. 

Poor insulation or inefficient ductwork may cause heated air produced by the heat pump to be lost, lowering overall temperatures which can cause the outdoor coil of the unit to freeze due to exposure from cold weather.

Having an adequately sealed atmosphere and well-insulated system will help keep the components free of ice buildup that could impede its functionality.

Investing In A Defrost Control Board Or Freeze Protection System

It can be a smart move to prevent heat pump freezing or its associated problems. 

Freeze protection system

A defrost control board controls the cycle of how and when a heat pump goes into the defrost mode while freeze protection systems provide additional safety monitoring and shut down the system before any damage occurs from prolonged icing up.

Temperature sensors

These systems typically come with temperature sensors that monitor both indoor and outdoor temperatures in order to determine how frequently they need to enter into and stay in their defrost cycles.


Not only do these devices help protect equipment, but they are also energy-efficient by using less electricity than manually initiating 12+ minute duties every few hours on top of regular operations costs.

Troubleshooting Frozen Heat Pumps In Winter

In winter, it is important to check thermostat settings, inspect ductwork for blockages, verify refrigerant levels and check the outdoor unit for issues in order to troubleshoot a frozen heat pump.

Check Thermostat Settings

The thermostat settings on a heat pump unit can be critical in preventing freezing. If the temperature setting is too low.

Additionally, if there are any issues with the thermostat such as inaccurate readings or incorrect wiring then that can also cause a frozen heat pump. 

To troubleshoot these issues it’s important for owners to take some time and inspect their thermostats regularly.

This involves checking for malfunctions like stuck sensors or dirt causing false readings, as well as ensuring that all wiring is properly connected. 

Inspect Ductwork For Blockages

Inspecting the ductwork of a heat pump is an important preventative measure to avoiding a frozen system. 

Blockages, such as dirt, debris and pet hair, can restrict airflow in through the system leading to inefficient performance and increased wear on its components.

Over time this will lead to poor functioning or complete breakdown of your equipment or even freezing up due to being unable to adequately expel trapped air within the coils.

Verify Refrigerant Levels

Verifying refrigerant levels is an important part of troubleshooting and preventing frozen heat pumps

When a system’s refrigerant level drops, the pres

sure decreases, causing the coil to become colder than usual until it starts freezing up.

Low refrigerant levels can also cause reduced cooling capacity in summer and unreliable heating during cold winter months. 

To check its fluid level, homeowners need to locate and open up the access panel on their heat pump unit to see if there is enough freon inside; alternatively.

Check Outdoor Unit For Issues

Regularly inspecting and maintaining the outdoor unit of a heat pump is essential to prevent frost-related damage. 

Issues with the outdoor coil, condensation levels or air flow can all lead to freezing of the system, which in turn has an effect on energy efficiency as well as the safety and performance of the heat pump.

Heat pumps are designed for colder climates but when temperatures fall too low it’s possible that coils will become coated in ice. 

Best Practices For Maintaining A Heat Pump To Prevent Freezing

Regular cleaning, professional maintenance, proper insulation and timely repairs are the best practices to maintain a heat pump and prevent it from freezing up.

Regular Cleaning

Regular cleaning and maintenance are essential elements in the prevention of a heat pump from freezing up. 

Dirty outdoor coils, air filters that aren’t regularly changed, inadequate airflow caused by blocked or closed vents, and insufficient refrigerant levels will cause a heat pump to malfunction and even freeze-up due to inadequate cooling capabilities.

Without regular cleaning accumulated dust and debris can quickly form on parts like evaporator coils causing it to absorb more heat than other components leading to an overall inefficient system.

Making it difficult for the unit to maintain comfortable temperatures efficiently affecting its performance during cooler months.

This is where professional maintenance comes into play as most manufacturers recommend annual HVAC check-ups specifically designed for your model’s needs.

Professional Maintenance

Regular professional maintenance for heat pumps can help prevent costly repairs and premature failure due to freezing. 

During a professional service, technicians perform several tasks that are critical in protecting the system from freezing up.

These include,

  • Checking the air filters
  • Inspecting gutter systems
  • Testing refrigerant levels
  • Examining fan blades and motors
  • Performing diagnostic tests to identify any potential issues before they become serious problems.

In addition to preventing freezes, regular maintenance helps maintain peak performance of your heat pump by improving energy efficiency, prolonging its life span, and ensuring that all components are operating effectively.

The cleanliness of air filters can also be addressed while replacing them with new ones if necessary.

Proper Insulation

When it comes to keeping a heat pump running efficiently, proper insulation is key. 

Insulation helps maintain consistent temperatures in the home and provides an air seal that minimizes airflow.

A well-insulated home can help reduce heating costs, prevent drafts, and control moisture levels inside the house – all of which are important for preventing a heat pump from freezing up.

Areas like windows, doors and weather stripping should be inspected regularly for any gaps or tears to ensure that there is no unnecessary air exchange with the outside environment.

Timely Repairs

When it comes to keeping a heat pump running optimally, timely repairs and maintenance are essential. 

Neglecting routine service appointments can lead to major problems such as a frozen or ruined heat pump due to components malfunctioning or excessive condensation build-up.

Heat pumps that have ignored signs of malfunctioning, such as noise from the motor, low heating or cooling capacities, cold temperature in spite of setting the thermostat higher/lower, ice build up on outdoor units.

Examples include dirty evaporator coils leading to inefficient cooling capacity; faulty fan blades resulting in restricted airflow.

Insufficient refrigerant levels causing various problems including increased energy costs.

Clogged air filters blocking optimal airflow; and many other issues caused by time -to-time worn out components that need replacement promptly.


Why does my heat pump keep freezing up?

The most common cause of a frozen heat pump is an airflow obstruction caused by clogged air filters or vents, which can limit the amount of air traveling over your unit and make it more likely to become too cold and freeze up. 

Additionally, low refrigerant levels in older units may also be responsible for ice forming on outdoor components.

What should I do if my heat pump freezes?

If you notice that your heat pump is icing up you should begin by performing a visual inspection to check for any potential blockages such as debris from plants or animals that could be obstructing the flow of air through the system, then follow up with professional maintenance/repair.

How often should I service my heat pump? 

Regularly scheduled maintenance is important to ensure optimal performance & efficiency so professionals can thoroughly inspect every component while identifying small problems before they develop into large ones saving time and money long-term.

Will servicing help reduce future freeze-ups? 

Proper servicing helps ensure all internal components are functioning properly without any underlying issues which makes it less likely for sudden drops in temperature to cause icy buildup around external parts etc


In conclusion, it is important to keep your heat pump well-maintained and monitored in order to prevent freezing. Insufficient airflow, low or empty refrigerant levels, excess moisture, dirty air filters, a malfunctioning defrost control board and damaged fan blades are all common causes of freeze-ups.

Heat Pump