As the weather starts to get colder and the temperatures start to drop below freezing, you may notice that your heat pump or HVAC goes through a defrost cycle. This is a normal part of the heat pump’s operation, and it helps to keep the heat pump running smoothly and efficiently.

When the defrost system switches on a lot of homeowners get confused and think that their heat pump is broken, but this is not the case. In fact, the defrost cycle is a vital part of the heat pump’s operation.

The heat pump defrost cycle kicks in when the outdoor coils start to frost over. This is because as the temperature outside starts to drop, the moisture in the air starts to condense on the cold coils. This can reduce the efficiency of the heat pump and cause it to work harder to maintain the desired indoor temperature.

This article will explain how the defrost cycle works, what causes it to happen, and how you can tell if it is working properly.

Types of Heat Pumps

There are three main types of heat pumps connected by ducts: air-to-air, water source, and geothermal ground source.

Air-to-air heat pumps are the most common type of heat pump. They use the air outside to heat and cool your home.

Water source and geothermal heat pumps are less common, but they are more efficient.

Water source heat pumps use water from a lake, river, or well to heat and cool your home. Geothermal heat pumps use the ground to heat and cool your home.

Related: Heat Pump Advantages and Disadvantages

What Is the Defrost Cycle and Why Do We Have Defrost Systems?

In heating mode, a heat pump pulls heat from the outdoors and transfers it indoors. The reverse is true in cooling mode.

As the heat pump pulls in air from the outdoors, it passes over coils that contain a refrigerant. This refrigerant absorbs heat from the air and turns into a gas. The gas is then compressed, which raises its temperature. The hot gas is passed over indoor coils, where it transfers its heat to the air inside your home.

This process continues until the outdoor coils start to frost over. When this happens, the heat transfer process is reduced, and the heat pump has to work harder to maintain the desired indoor temperature.

The defrost cycle kicks in when the frost on the outdoor coils starts to build up.

How A Heat Pump Defrost Cycle Works

The defrost cycle works by reversing the flow of refrigerant. The refrigerant is still compressed, but instead of being passed over the indoor coils, it is passed over the outdoor coils.

This melts the frost on the coils and clears any debris that may have built up. Once the frost is melted, the heat pump can start working normally again.

This is where the heat come from for defrosting. The heat for the defrost cycle comes from the compressor. The compressor is a vital part of the heat pump, and it is what pumps the refrigerant around the system.

How can you tell if a heat pump is defrosting?

You can tell if your heat pump is defrosting by a flashing light on the unit and once the fan has stopped. The reversing valve will also change directions.

If you are still unsure, please consult your heat pump’s manual or call a professional for assistance.

What causes the defrost cycle to Kick In?

The defrost cycle is triggered by two things: time and temperature.

Most heat pumps have a built-in timer that tells the unit when to go into defrost mode. This timer is usually set to activate the defrost cycle once every 12 hours.

The second trigger is temperature. The outdoor coils must be below freezing for the defrost cycle to kick in. This is because the frost only forms on the coils when they are cold enough.

Does a Heat Pump Dehumidify

Yes, a heat pump can dehumidify your home. The defrost cycle is one way that a heat pump removes moisture from the air.

During the defrost cycle, the heat pump reverses the flow of refrigerant. This causes the refrigerant to absorb heat from the air instead of releasing it. As the refrigerant absorbs heat, it also absorbs moisture. This moisture is then condensed and removed from the system.

The defrost cycle is not the only way that a heat pump can remove moisture from the air. The heat pump also has a built-in dehumidifier.

The dehumidifier works by cooling the air below its dew point. This causes the water vapor in the air to condense and be removed from the system.

The dehumidifier can also be used in cooling mode. When the air is cooled below its dew point, the moisture in the air condenses and is removed from the system. This helps to keep your home cool and comfortable during the summer months.

Does a heat pump dehumidify in winter?

Yes, in the colder months when the heat pump is in use more to maintain comfortable temperatures in the home, it will also be working to remove moisture from the air.

The defrost cycle and the dehumidifier both work to remove moisture from the air. The defrost cycle removes moisture during the heating cycle, and the dehumidifier removes moisture during the cooling cycle.

Do heat pumps dehumidify when heating?

No, a dehumidifier ins not needed in this scenario. The room will automatically dehumidify when the heat pump is in cooling mode. There is no requirement for the heat pump to dehumidify while it’s operating in heating mode. Warm air circulating throughout the space removes any moisture from the air.


How to defrost a heat pump in winter

Luckily, your heat pump will do this automatically! There’s no need for you to do anything. It will be set on a timer or will switch on if it detects that the outdoor coils are below freezing.

What is the difference between a heat pump and an air conditioner?

An air conditioner cools the air in your home by circulating refrigerant through a closed-loop. A heat pump does this as well, but it can also reverse the process to heat your home.
In heating mode, a heat pump circulates the refrigerant through a loop. The refrigerant absorbs heat from the outdoor air and transfers it indoors. In cooling mode, the process is reversed. The refrigerant absorbs heat from the indoor air and transfers it outdoors.

Related: Air Conditioner (AC) is Short Cycling (HOW TO FIX IT)

What happens if the heat pump doesn’t defrost?

If the heat pump doesn’t defrost, it will eventually stop working altogether. The coils will be too frosted over and the unit won’t be able to function.

Can I turn off my heat pump’s defrost cycle?

No, you cannot turn off the defrost cycle. It is an important part of the heat pump’s operation and is necessary for the unit to function properly.

Why does my heat pump run constantly in winter?

There are several reasons why your heat pump might be running constantly in winter. One reason could be that the outdoor coils are frozen over. This restricts the airflow and makes it difficult for the heat pump to operate. Another reason could be that the thermostat is set too low. The heat pump will run until it reaches the set temperature, even if that takes a long time.

Can I defrost my heat pump myself?

Yes, you can turn on the fan to help defrost the outdoor coils. However, it’s best to leave this to a professional. Frozen coils can be a sign of a bigger problem, such as a refrigerant leak. A professional will be able to diagnose and fix the problem so that your heat pump can operate properly.

How often should a heat pump cycle on and off

A heat pump should cycle every hour or two on average. The cycle should last 10 to 20 minutes. A heat pump will constantly run during cold outside temperatures (below 30-40 degrees Fahrenheit).

Heat pump leaking water outside unit in winter, what can you do?

If this is the case, this is the job for a professional. This could be a sign of a bigger problem, so it’s best to have someone take a look at it who knows what they’re doing.

About the Author

Passionate about helping households transition to sustainable energy with helpful information and resources.

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