Defrost A Heat Pump: Step-By-Step Instructions

Photo of author

By Debarghya Roy

Table of Contents

To introduce you to the world of heat pumps, let’s talk about what they are and why you may need to defrost them. A heat pump is a heating system that moves warm air to heat your home. 

In this subsection, we will cover the definition of a heat pump and why it’s important to defrost it regularly.

Definition of a Heat Pump

A Heat Pump is a device that transfers thermal energy from one place to another. It uses mechanical work and electricity to move heat from a low-temperature source to a high-temperature sink.

how to defrost a heat pump

 What Is a Heat Pump Defrost Cycle?

A heat pump’s defrost cycle is a critical process that removes frost buildup on the outdoor coil which may interfere with its heating process. 

 How Does a Heat Pump Defrost Cycle Work?

During defrost mode, the outdoor fan shuts down, and the system briefly reverses the flow of refrigerant, which creates warm air to melt any frost on the coil. 

how to defrost a heat pump

A defrost sensor checks the coil temperature, and if it rises high enough to signal no frost condition, the defrost cycle ends, and the heating cycle resumes.

Defrosting is a necessity for heat pumps. During the ‘Thawing Mechanism’, the heat pump changes to defrost mode to melt snow and ice that accumulates on outdoor coils.

Control systems can be programmed differently, depending on the situation or equipment.

Why is Defrosting a Heat Pump Necessary?

To maintain your heat pump’s optimal performance, defrosting is necessary during winter. 

Low temperature and high humidity can lead to frost on the outdoor coil, resulting in energy inefficiency and damage to the system.

Heat pumps transfer indoor heat to outdoor air. However, frost buildup on the outdoor coil can reduce its capacity to transfer heat.

So you must remove the frost periodically. When in defrost mode, the system switches from heating mode to cooling mode briefly.  

Benefits Of Defrost Cycle For Heat Pump

Defrost Cycle is a must for a Heat Pump’s performance. Warm air is sent over the outdoor unit’s coils to melt ice during the cycle. This is a necessity, as ice blocks airflow and can harm the unit.

This process runs every 30-90 minutes based on the outside weather and lasts 5-10 minutes. It is done while in heating mode and interrupts heat production to get rid of the ice.

Defrost Cycle saves energy by avoiding ice from blocking the airflow. A study by Energy Vanguard has proven that an inadequate Defrost Cycle can affect the system’s performance.

ASHRAE Journal states that even with regular maintenance, systems older than one year will present a 5-15% decrease in efficiency. Don’t let frost mess up your Heat Pump! Stay hot and keep it running.

Defrost Cycle Components

To defrost a heat pump, there are several components that work together. 

These pieces include a defrost thermostat, reversing valve, compressor lockout delay timer and an electric heater. 

We can create a table to illustrate how these parts function. It’ll show their location within the system and what they do.

Defrost ThermostatOn outdoor coilMeasures outdoor air temp for triggering
Reversing ValveIn front of compressorDiverts refrigerant flow direction
Compressor Lockout Delay TimerIn control box/boardDelays heating during defrost cycle
Electric HeaterBelow condenser coils/drain panMelts ice on coils

Outdoor Temperature Sensor

The outdoor temperature sensor is essential for the heat pump to defrost the cycle. 

It measures and sends data to the heat pump, and regular maintenance and cleaning are vital for its proper function. Incorrect data can lead to wasted energy and higher bills.

Defrost Sensor

The defrost sensor is a key part of the heat pump defrost cycle system. It detects when frost forms on the outdoor coil and triggers the defrost cycle. 

Its location is near the intake section of the outdoor coil. Its operational range is between 5℉ and 55℉ and its electrical resistance is between 2000 and 10,000 ohms.

To make sure the defrost sensor works properly, check the wires for dirt or corrosion regularly

Also, watch indoor humidity levels as high humidity can cause frosting problems on the outdoor unit.

Plus, install a backup defrost timer that kicks in after four hours of reversed heating mode, if the primary defrost control system fails. 

This improves efficiency when temperatures drop and maintains steady energy use without overworking the compressor.

Outdoor Fan

The outdoor fan is a must for the heat pump defrost cycle. It kicks in to blow cool air over the outdoor coil, aiding in dehumidification and keeping ice away.

  • When the defrost cycle starts, the outdoor fan turns off – hot refrigerant melts ice on the outdoor coils.
  • Once melted, the heat pump goes back into reverse mode ’till all frost is gone.
  • The outdoor fan then turns on again to help dehumidify and drain away surplus liquid.

Circuit Breaker

The ‘.5 Refrigerant Valve’ is safeguarded by a circuit breaker. It wards off harm to the compressor and motor. 

The correct rating for a defrost cycle depends on the heat pump’s size and maker’s instructions.

The following table shows the circuit breaker rating for different heat pump sizes:

Heat Pump SizeCircuit Breaker Rating
1.5 ton15 amps
2-3 tons20 amps
3.5-4 tons30 amps

Selecting the right breaker size is essential for a defrost cycle. Wrong sizing can cause the breaker to trip often, damaging the compressor and motor.

Circuit breakers must be properly managed for a smooth running heat pump. This is key for long life and energy efficiency. Exterior components should also be cleaned routinely.

Reasons for Heat Pump Freeze-up

To understand why your heat pump freezes up, look no further than these reasons,

Common Culprits

Heat Pump Freeze-up can be caused by various factors. These include insufficient airflow, clogged air filters, lack of regular maintenance, inadequate refrigerant charge, broken or malfunctioning sensors, and faulty defrost control boards and relays.

Low outdoor temperature, humidity levels, and dirt accumulation can also trigger Freeze-up. An accurate diagnosis is necessary to resolve this issue.

Ignoring the culprits can lead to system damage and higher energy bills. It’s best practice to avoid overworking the Heat Pump and scheduling routine checkups with certified technicians.

A study by NREL found that regular maintenance helps keep up to 95% of the Heat Pump’s original efficiency after five years. Winter finally realized it forgot to turn off the AC, causing a Freeze-up.

Low Outdoor Air Temperature

When winter strikes, heat pumps often freeze up. This is because the outdoor air temp falls below the level the pump’s design and size can handle. 

The colder it is outside, the more likely the water inside the heat pump coil will freeze. 

To stop this from happening, homeowners can insulate their heat pump or use a specialized model made for cold climates.

Maintenance and servicing also help prevent freeze-ups. 

If defrosting doesn’t help, expert help is needed. Professional heating technicians should inspect the thermostat and refrigerant levels.

Frost Conditions

When the temp drops, frost accumulates on the outdoor coil of a heat pump. 

This can lead to decreased efficiency or even complete freeze-up, forcing the pump to switch off automatically. 

To prevent this, ensure good airflow and proper insulation. A defrost controller can help with energy efficiency and longer pump life. 

Cleaning and maintaining the outdoor unit is also key. Trim back nearby trees or bushes for proper air circulation. 

ENERGY STAR says regular maintenance can reduce energy costs by up to 30% and extend equipment lifespan. Water vapor is great for saunas, but your heat pump needs proper airflow to prevent freeze-up.

Water Vapor

Water vapor can be a major cause of heat pump freeze-up. When temperatures drop below freezing, water vapor in the air sticks to the heat exchange coils of the pump. This usually happens in winter and can damage the system.

It’s important to have a dry environment around the heat pump. Proper insulation and leak sealing can stop moisture gathering.

Maintenance and inspection by professionals can spot any water vapor issues before they start. 

Ventilation and dehumidification can also lower humidity levels and reduce the risk of freeze-ups.

Operator Error

Improper handling of heat pumps can lead to operator errors. These can happen due to lack of knowledge, training or experience. 

This can cause damage to the system, Common mistakes include: 

  • Setting incorrect thermostat levels 
  • Running the unit continuously 
  • Not cleaning the air filter

This can lead to system overload and freeze-ups.

It is important to know the components of a heat pump and how it works. Plus, maintenance tasks such as 

  • Keeping the evaporator fins clean
  • Checking the refrigerant levels  
  • Oiling the bearings regularly

Preventative Measures For Heat Pump Defrost

To avoid freeze-ups in heat pumps, preventative measures must be taken. Such as:

  1. Maintaining the defrost cycle,
  2. Cleaning the outdoor coil,
  3. Checking refrigerant levels,
  4. Replacing air filters frequently and ensuring good airflow around the unit.

A homeowner ignoring heat pump maintenance led to severe damage due to a prolonged freeze-up. 

This serves as a reminder to prioritize preventative measures and maintenance to avoid costly repairs and maintain optimal performance.

Regular Maintenance

Keep Your Heat Pump Warm and Toasty: Regular Maintenance is Key!

  • Cleaning or replacing air filters every one to three months guarantees good airflow and prevents dirt buildup.
  • Inspect and clean outdoor coils regularly to remove debris such as dirt, grass clippings, and leaves.
  • Check refrigerant charge yearly for optimal performance.
  • Secure electrical connections without fraying or damage.
  • Hire a professional for an annual checkup to address underlying issues.
  • Debris on top of the unit can also lead to freeze-ups.

Best Solution for Cold Weather

When it comes to cold weather, heat pumps are at risk of freezing up. To prevent this, here are a few solutions:

  • Ensure proper airflow. Keep outdoor units clear of snow and debris. Indoors, check vents and filters aren’t blocked.
  • Install auxiliary heating devices. Space heaters can keep your home warm in winter.
  • Maintain regular system maintenance. Inspections and annual maintenance can spot potential problems early.

Remember, these measures work best when used together. In some cases, you may need further help. Consulting an HVAC pro can diagnose complex system issues.

A combination of preventative measures and maintenance can make sure your heat pump works in winter. Don’t get caught out – use these steps and thaw it like a pro!

Steps to Defrost a Heat Pump

To defrost your heat pump, follow these steps with the sub-sections as a solution. 

Switch off the Heating Cycle

To freeze-proof your heat pump, initiate the defrosting process! Stop the heating cycle. This is critical to stop any ice buildup. Follow these steps:

  1. Access the control panel.
  2. Select the switch-off option.
  3. Check the indicator light or display.
  4. Wait a few minutes.
  5. Adjust the thermostat to remain comfortable.
  6. Wait until it is entirely defrosted.

Cover your outdoor unit with a tar or blanket. This can help keep heat and speed up thawing. 

Check the Outdoor Coil and Fan

For a heat pump to work properly, its outdoor components need special attention during defrosting. To check them, follow these steps:

  1. Turn off the power.
  2. Check the fan blades for debris or damage.
  3. Clear any obstructions from around the outdoor coil.

Wear protective gear like gloves and goggles for safety.

Know about cleaning chemicals too.

Excess system operation in cold weather may cause increased energy consumption. 

As per Energy Star, using an air-source heat pump instead of a furnace or A/C in cold locations can save 30-40%

Turn on the Fan Mode

Turning on the Air Circulating Mode is key to defrosting your Heat Pump. Here’s how to do it in 3 simple steps:

  1. Locate your thermostat and access the settings menu.
  2. Select ‘Fan’ and choose the ‘On’ option.
  3. Wait for the system to start circulating air. This will help melt any ice buildup and defrost your Heat Pump.

Allow the Defrost Cycle to Work

Defrosting your heat pump is necessary for it to work efficiently and provide comfort. To do so, follow these steps:

  1. Set the thermostat to “emergency heat” mode.
  2. Wait 15 minutes for the system to shut down.
  3. Inspect the outside unit for ice buildup or debris.
  4. Switch your unit on again and wait until it completes one full cycle of defrosting.
  5. If there is still ice accumulation in the outdoor unit, repeat steps 1-4 or call a technician.
  6. Revert all settings back to normal.

Interrupting the defrost cycle could decrease efficiency and put extra wear and tear on the system. 

Check the manufacturer’s recommendations before doing anything else. According to Energy Star, an efficient heat pump can save up to 20% on heating costs. Don’t let your ex mess with the thermostat.

Verify Desired Effect

When thawing a heat pump, it’s crucial to reach the desired result. 

All ice and frost on the unit should be completely melted and taken away. Plus, the unit should be running optimally before it’s put back into use.

To check the desired effect, inspect the unit after thawing. Look for any remaining ice or frost inside and outside of the unit. 

Listen for any strange noises or odors coming from the unit. And, make sure that when you turn it back on, it runs smoothly.

Once you’ve successfully verified the outcome, it’s wise to discard any melted ice and leftover water properly, prior to using the heat pump again.

Additional Steps (For Older Heat Pumps)

Before defrosting an old heat pump, you need to consider extra steps.

  1. Check for any damage.
  2. Turn off all power and remove leaves or debris from the area.
  3. Increase air flow with fans and use built-in heat strips to melt ice.
  4. Follow manufacturer instructions. For newer models, refer to the manual.
  5. Also, check pressure sensors for rust.

Tips for Efficient Heat Pump Defrosting

To efficiently defrost a heat pump for optimal performance, you need to keep in mind a few important factors.

First, avoid defrosting in direct sunlight, as it may interfere with the heat pump’s defrost cycle. 

Avoid Defrosting in Direct Sunlight

When it comes to efficient heat pump defrosting, direct sunlight can be a strain. To avoid this, follow these four steps:

  1. Position your unit away from things that could create shadows, like trees or buildings.
  2. Install shades, awnings, or umbrellas above the unit.
  3. Look for when the sun is weak and plan defrosting then.
  4. Use a fan setting that will improve airflow over the coils.

“Energy Star” states that frost build-up reduces efficiency and makes them less effective in regulating interior temperatures. To get the best performance, ensure your heat pump is clean and fresh.

Keep the Outdoor Air and Coil Clean

  • Maintaining outdoor air and coil cleanliness is vital for efficient heat pump defrosting. Dirt, debris, and other particles can reduce airflow, leading to higher energy use. 
  • Cleaning the coil and filter regularly prevents dust buildup. Dirty coils can cause system breakdowns
  • Corrosion or rust on the coils should be prevented. Saltwater spray can form a coating on copper tubing, decreasing its efficiency and increasing energy consumption.

Monitor Relative Humidity

It’s critical to keep optimal levels of humidity for a heat pump to work properly. 

Low humidity can cause frequent defrost cycles, wasting energy and lowering efficiency. 

High humidity can lead to ice formation on the outdoor unit, damaging the equipment and reducing heat transfer.

Use a hygrometer or a thermostat with a humidistat to measure relative humidity. Ideally, it should be kept between 30% and 50%

Check readings often and adjust accordingly. See the table below for effects of varying levels of humidity on heat pump efficiency.

Relative HumidityEffect on Efficiency
Below 30%Too frequent defrost cycles, increased energy consumption
Between 30% and 50%Optimal conditions
Above 50%Ice accumulation on outdoor unit, reduced heat transfer efficiency

Check Coil Temperature

Track temp for effective heat pump de-icing! To get the most out of defrosting your heat pump, monitor the temperature of its coils. This will help you save energy and avoid damage. Here are some tips to keep your pump’s temp in check:

Check coil temp: Use a table to track the temp during defrosting. Sample table below:

TimeInlet TempOutlet Temp
0 min20°C27°C
10 mins16°C34°C
20 mins14°C35°C

Use a Garden Hose

A Water Hose can be an effective way to defrost heat pumps. Here’s a 3-step guide on how to use a Garden Hose efficiently:

  1. Switch off the power source.
  2. Position the hose at an appropriate distance from the device.
  3. Turn the nozzle to a high-pressure stream and spray the heat pump from different angles.

Don’t spray hot water onto the heat pump, be careful near any electrical parts.

Keep your garden hose clean before and after use, debris can clog up the nozzle.

This simple process can save you money. One homeowner saved $800 in heater repairs annually. So, take good care of your heat pump and reap the rewards.


To ensure the efficient operation of your heat pump, you need to take the defrost cycle into consideration. After exploring the different steps to defrost a heat pump, you may now know that knowing your HVAC system is important. 

Frequently Asked Questions

What causes my heat pump to freeze up during cold weather?

The common culprit of a frozen heat pump is water vapor turning into frost on the outdoor coil due to outdoor temperature and relative humidity. 

The frost condition affects the heat pump’s defrost cycle, causing it to operate more frequently than usual or even fail. Operator error such as shutting off the circuit breaker to the outdoor unit in cold weather or faulty sensors can also contribute to a freeze-up.

What is the best solution to defrost a frozen heat pump?

The best effort to defrost a frozen heat pump is to turn off the heating system and switch to air conditioning mode. This allows the outdoor unit to melt the frost, which can take a few hours to complete. 

Alternatively, using a garden hose on the outdoor coil may speed up the defrost process.

How can I prevent my heat pump from freezing up?

Preventative measures to keep your heat pump from freezing up include keeping the outdoor coil free from debris and obstructive objects that block airflow. Avoid installing the outdoor unit in direct sunlight and protect it from harsh weather conditions. 

What happens if I run my heat pump in defrost mode continuously?

If your heat pump system continually runs in defrost mode, it can reduce the efficiency of the heating cycle and increase energy consumption. Running the defrost cycle work unnecessarily can also shorten the lifespan of the outdoor fan motor and compressor, leading to costly repairs or replacements.

Can I manually defrost the outdoor coil of a heat pump?

You can manually defrost the outdoor coil of a heat pump. However, you need to take extra caution to avoid damaging the coil with a sharp object during defrosting. Follow the above steps and consider wearing gloves to protect your hands.

What is a heat pump defrost?

A heat pump defrost is a function that reverses the heat pump cycle to melt any ice that has built up on the outdoor unit.

What causes a heat pump to freeze?

A heat pump can freeze due to various reasons, including low refrigerant levels, dirty air filters, a malfunctioning outdoor fan, or extremely cold weather conditions.

How do I know if my heat pump is frozen?

You may notice that the heat pump is not providing enough heat to your home or that the outdoor unit has a layer of ice on it. If you suspect your heat pump is frozen, it is best to have it inspected by a professional.

Can I defrost a heat pump manually?

You can manually defrost a heat pump by turning off the power to the unit, using a gutter to remove any ice on the outdoor unit, and turning on the heat pump with water to melt any remaining ice.

How often should I defrost my heat pump?

Your heat pump will go into a defrost cycle automatically as needed, typically every 30-90 minutes in colder weather. If you notice that the defrost cycle fails or isn’t working properly, you’ll need to call a professional to repair it.

What should I do if my heat pump is frozen?

If your heat pump is frozen, turn off the unit and wait for the ice to melt. If the weather is just right, the ice melts on its own within a few hours. You can also manually defrost the unit as described above, but it is best to have a professional inspect the unit to determine the cause of the freezing.

Can I turn the heat pump off during a defrost cycle?

You should not turn the heat pump off during a defrost cycle as it can cause damage to the unit. It is best to let the unit complete the cycle and turn back on once the cycle is complete.

How do I turn the fan on during a manual defrost?

To turn the fan on during a manual defrost, switch the thermostat to the “fan on” setting. This will turn the fan on without activating the heat pump.

Why is my heat pump’s defrost mode not working?

The defrost mode on your heat pump may not be working properly for several reasons, including a malfunctioning defrost thermostat, a faulty outdoor temperature sensor, or a malfunctioning control board. It is best to have a professional inspect and repair the unit.

How can I prevent my heat pump from freezing?

You can prevent your heat pump from freezing by regularly changing the air filter, cleaning the outdoor unit, and ensuring proper refrigerant levels. It is also important to keep the area around the outdoor unit clear of snow and debris.

Heat Pump