Heat Pump Freezing Up? What Causes It Iced Up And How To Fix It

Back in the 1990’s heat pump technology got to a point where they were becoming very energy efficient. So much more so than other home heating equipment that was powered by fossil fuels such as gas or oil and electricity. This made heat pumps become a popular choice and their sales took off dramatically. They also offer the advantage that many models can produce cool air too by reversing their refrigerant flow. There is one inherent problem with heat pumps though and that’s when they are producing heat certain conditions would sometimes make them freeze up.

It’s normal for the outer evaporator coils on a heat pump to get cool during the heating process. It’s not however normal for those same evaporator coils to get so cool that they freeze over and stop the heat pump from working and can potentially damage it. In this article, we will explain how a heat pump works, why it’s outer coils sometimes freeze over and steps you the homeowner can take to try and prevent this from happening.

Understanding First How a Heat Pump Works

Many of you have probably been using your heat pump for years and are probably very familiar with how they work. For those of you who aren’t here is a quick overview of how your heat pump works.

Heat pumps contain a refrigerant that is under different pressures in various parts of the heat pump that allow them to heat or cool air. At some parts of the heating and cooling process in a heat pump this refrigerant is a liquid and sometimes it’s a gas. It’s this change in the liquid or gas state of the refrigerant that allows a heat pump to collect warm air and take it in or out of your home.

Here is a quick summation in layman’s terms as to how a heat pump collects and transfers heated air:

· How a heat pump warms the air in your home?

First of all, at no part in the heating process of your home does your heat pump actually generate any type of heat itself. It does not have a heat source such as a gas, electric or oil heater does. You should think of it as more of an air transfer device. Even when it’s cold outside there is still available heat in the air. Your heat pump captures this available heat and transfers it into your home.

· How a heat pump cools the air in your home?

A heat pump cools your home by simply reversing the heating process. Just as your heat pump was able to capture the heat of the outside air so too can it capture the heat that is in the air inside your home. When it removes the heat from the air inside your home it leaves your home much cooler than it normally would be if you did not own a heat pump.

Why Did Your Heat Pump Freeze Up?

Heat pump freeze up is never considered normal under any circumstances. There is always an internal or external source of the problem. That’s because heat pumps have sensors in them that trigger an automatic defrost cycle if they detect the exterior evaporator coils are starting to build up ice.

You also must know that there is no one specific reason that is the sole cause for heat pump freezing up. There are actually 5 different reasons as to why your heat pump exterior coils can freeze over. They consist of the following:

1. Technical Malfunction

Even though a heat pump works on simple principles of physics in actuality it’s a complicated device with many moving parts. Part of the system is also exposed to some pretty harsh elements throughout the year depending on where you live. Because of these factors and not unlike other types of heaters, it’s not uncommon for a part on a heat pump to fail as it ages.
Here are some of the technical problems that can cause your heat pump to freeze up that will necessitate you giving an HVAC professional a call to correct them:

  • Low refrigerant levels/Refrigerant Leaks
  • Malfunctioning defrost cycle
  • Bad sensors or thermostats
  • Malfunctioning electrical relays for the defrost system
  • Stuck cycle reversing valve
  • Damaged or poorly operating fan motors

2. Restricted Airflow

One of the most important aspects of a heat pump being able to heat or cool the air in your home is airflow. It not only moves the heated air inside your home but it also is the catalyst for the process that allows your heat pump to capture heat from the outside air.

When this airflow becomes restricted it does not allow air to pass over a heat pump’s outer evaporator coils sufficiently. This allows the coils to cool to an unusual temperature that is conducive to heat pump freeze up.

Examples of major causes of restrictive airflow are such conditions as leaves and branch debris buildup around your heat pump or a clogged air filter on your heat pump system.

3. Excess Moisture

Water buildup and extra moisture that gets trapped in your heat pump area are not your friends. Conditions such as a broken gutter allowing excess water to pour directly onto your heat pump and ponding of water at the base of your heat pump can significantly increase the chances of your heat pump freezing up.

4. Lack of Routine Maintenance

Although most heat pump models are very well-built and will last you a very long time, they still need to have routine maintenance done on them. Having this routine maintenance done on a yearly basis will help keep your heat pump in very good working order. This is usually a service that most HVAC companies will do for a very reasonable price also.

During a heat pump service call an HVAC technician will do several important maintenance tasks. These include such things as cleaning or replacing the systems air filters, cleaning the exterior evaporating coils on the heat pump and lubricate the all-important fan motor. Simple maintenance steps such as these can greatly extend your heat pumps useful life and help prevent it from ever freezing up too.

5. Settling

Settling of your heat pump slab can cause the exterior of your heat pump to become exposed to standing groundwater or cause it to tip into an area where excess water runs onto it. These are never good things for your heat pump and this exposure to excess moisture can significantly increase your heat pump’s chances of freezing up.

As we will discuss later on, 3 of the 5 contributing factors on this list that cause heat pump freeze up (restricted airflow, excess moisture and settling) can often be corrected rather easily by you the homeowner.

Steps a Homeowner Can Take to Prevent Heat Pump Freeze Up

There are some steps you as a homeowner can take to help prevent your heat pump from ever freezing up in the first place.

They include the following:

· Periodically check your heat pump system’s air filter

We mentioned before that poor airflow is one of the major causes of heat pump freeze up. If the air filter on your heat pump system is clogged or dirty it can significantly cut down on the air flow. Clean and replace your air filters as necessary.

· Make sure the air vents and cool air intakes in your home are not blocked

This is another way that air flow can be cut down significantly in your heat pump system and lead to it freezing up. Never put furniture to close to air vents and registers and make sure you do not pile boxes or other objects in front of them too.

· Relevel your heat pump slab if necessary

Not only is it important that your heat pump is level to prevent freezing but it helps keep other internal parts from getting damaged as well. Most heat pump slabs can be easily leveled by gently lifting them with the end of a pointed shovel and then placing patio blocks under the slab so it will stay level.
Your heat pump concrete slab should also always be at least a few inches above ground level to prevent puddling water from getting into your heat pump too.

· Keep leaves, grass clippings and other debris away from your heat pump

Here is another condition that can both restrict airflow in your heat pump system and cause excess moisture to accumulate around it. We already know these are two conditions that greatly contribute to heat pump freeze up. So keep such things as organic material, snow, branches, dirt and other undesirables from building up around your heat pump area.

· Repair broken gutters and clean overflowing ones that are feeding water onto your heat pump

When gutters become clogged with leaves they can overflow onto your heat pump and cause it to freeze up. Fix broken gutters that are over your heat pump and channeling water onto it too. If you have no gutters on your house think about installing them so water does not run onto your heat pump too.

· Schedule routine heat pump maintenance

For the little money you will spend on a heat pump service call it will pay big dividends for the longevity of your heat pump. It will also go a long way towards eliminating conditions that can contribute to heat pump freeze up.

When is it Time to Call Your Local HVAC Technician?

There are times when homeowner care or professional maintenance simply does not prevent your heat pump from freezing up. If you find the exterior of your heat pump completely frozen over the best thing to do is shut it down and let it defrost. Of course, this will happen too slowly if the weather is very cold outside and you may have to call an HVAC professional to do this for you.

Also, if you defrost your heat pump and it quickly freezes up again, you most likely have a technical problem that will require a service call from an HVAC professional.

If you are not familiar with how to work on a heat pump yourself it’s always best to leave this task up to a professional HVAC technician. Keep in mind also that if you work on your heat pump yourself you may void any warranty you have remaining on it.

You can use our Free Estimate Tool to get at least 3 quotes in your location.

Routine And Preventative Maintenance Are the Key to Heat Pump Freeze Up Prevention

Without a doubt, the two best ways to help keep your heat pump from ever freezing up are yearly professional routine maintenance and preventive maintenance by you the homeowner.
Why have a professional do routine maintenance and cleaning on your heat pump every year? Think of it like changing your oil every so many miles on your car; it just helps to keep your heat pump in good working order. Many times HVAC professionals can correct small problems during a routine maintenance call that would have become bigger and more expensive repairs if they went undetected.

As we previously discussed you as a homeowner can help keep your heat pump from freezing up too. Keep the area around your heat pump free of air restricting debris and make sure conditions are not favorable for moisture buildup on or around your heat pump.

If you follow these simple steps you greatly reduce the chances that your heat pump will ever freeze up and leave you literally out in the cold.

Written by

Rene has worked 10 years in the HVAC field and now is the Senior Comfort Specialist for PICKHVAC. He holds an HVAC associate degree and EPA & R-410A Certifications.

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